After browsing this question on Brahma temples. I was wondering why even Yama temples are very few in the world. Yama is the god that determines whether a person(soul) is sent to Swarga lok (Heaven) or Naraka lok (Hell). Hence I assume that Yama would be worshiped a lot and was wondering why Yama temples are rare.
This is due to a curse pronounced on Dharmaraja by a Brahmin, when Yama killed his son as a part of His (Yama's) duty. This is explained in Chapter 139 Greatness of Dharmarajeswara Book 6 Nagarakanda of Skanda Purana.
Formerly, there was a Brähmana hailing from the family of Kasyapa in that holy spot. He was well-known as Upädhyäya. He was devoted to the Vedic lore. He begot a son later in his advancing age even as he strictly adhered to regular study of the Vedas. He acquired ample wealth. When only five years old that son expired causing great sorrow to his father and mother. On knowing that his son had gone to the abode of Dharmaräja, the Brähmaoa became angry with Vaivasvata (Dharmaräja). In his height of grief, he took some water in his hand. With mental concentration and personal cleanliness, he then pronounced a terrible curse on Dharmaräja. "Since I have been made a sonless person by that wicked-souled one, Yama, of defiled soul, he will also become sonless. Further people in this world will not perform worship to him nor glorify his name as in the case of other heaven dwellers. If anyone gets up early in the morning and recalls his name, there shall be obstacle in his auspicious activity."
Dharmaraja then pleads Lord Brahma to mitigate the curse. Lord Brahma creates Ailments to take lives of people after their destined life span.
27-30. Lord Brahma said: "O Yama, all these Ailments have been employed by me. They will always render help to you in all matters. Now if anyone reaches the end of his life-span these should be sent always by you to take his life. Thereby, the ignominy arising from the death of people shall devolve upon these alone on the earth and not on you. Therefore, at my behest, go to your own abode and be engaged in your duty. Undoubtedly, you will never incur a fault (sin)."
- Then the Son of Ravi took all those Ailments to his world and spoke to them respectfully:
32-34. "You shall regularly ask Citragupta and go to the earth for taking >away the life of people when the proper time arrives.
Lord Yama now returns the Brahmana son to Brahmana and son requests his father to take back curse.
The Brähmara said:
- O my son, my utterance can never be untrue even if it is jokingly made. It is all the more so if uttered by a grief stricken' one.
- Hence, O wise one, he will not get a son from the divine womb. due to my curse.
- He will have another son (one son will be born from Sudra women known as Vidura which is explained in previous chapter) born of the womb of a human female by means of Räjasüya and Asvamedha. He will redeem him.
- Of what avail is a son bom to one if he is not capable of redeeming the members of his father's family by performing excellent rites on the earth?
- As regards the curse uttered by me in regard to his worship earlier, O dear son, listen to what I say:
- His worship with various kinds of Mantras mentioned in the Vedas will not find a place on the earth at all, dear son.
- His worship shall be with Mantras composed by humans. It will be different from that of the other Devas. It is the truth that has been uttered by me.
This son is none other than the Yudishtara, the eldest Pandava.
Regarding the story of Vidura, Dharmaraja was cursed by Sage Madavya to take birth from Sudra women. Sage Mandavya was leper and due to severe penance of his chaste wife Dhirgika, he gets relieved of Leprosy. He then inquires Lord Yama the reason for his leprosy. Lord Yama says that mandava pierced a crane with tip of spear in one of his previous births and as a result of it he was born as leper. On hearing the words of Yama, Mandava gets infuriated as he considers punishment of leprosy is unfair for such a small deed. He curses Yama to born from womb of a Shudra. Later Yama prays to Shiva and Shiva grants boon to Yama that though he will be born from womb of Shudra (Vidura), he will be man of righteous temperament.
Son of Brahmin composes a mantra for Yama beginning with "Sugam nah panthah". This story happened at Dharmeswara linga and people who pray Yama statue, installed by son of Brahmana, at this place with the above Mantra will never die prematurely.
So, due to above curse, worship of Yama is rare like Brahma.
Brahma's story is different than Yamadeva. Shiva banned worship of Brahma so many people accepted it.
Any number of temples are based on the the way how much the deity is favorite of how many people?
If people are more, more temples, if less, less temples.
In Hinduism most deity has some territory in India, like Ganesha is widely worshiped in Gujarat and Maharashtra, you will find more temples in these regions.
Lord prabhu Kartikeya is widely worshiped in south, in Gujarat there is not even single temple of Lord Kartikeya, but it does not mean they avoid this deity, when ever they will pass through this Lord Kartikeya's temple they will go there and will salute Lord Kartikeya. Temples are not there because people did not build any.
Mother Durga is widely worshiped in Bengal side and more temples are there only.
Except Shivalinga temples most of the deity has their number of devotees in specific regions.
It is because the playground of those deities are there. Most famous temples have related story of the deity. That connects people's faith to that deity.
Yamadeva is deity who is called
YamaRaja. There is nothing like he has less importance than others. Of course he is worshiped. But the number of temple are less because of less attention of people to him, and less people have him favorite.
Any Hindu will go to his temple, but the number of temples increases with people's faith with the deity.
You will find almost 100% people knows Hanuman Chalisa but rarely 2% who know some verse of Yamadev. May be in some territory Yamraja's temples and devotees may be more. But if we consider the whole India, the knowledge about this deity will be less compared to Shiva, Rama, Hanumanaji temples.
People does not worship based on what deity's work is, they worship based on the faith.
Devotee may select any form of GOD, all are GOD only. may be yamaraja's form is less people chosen.
More people have more faith in Shiva so they will build more Shiva temples , yes they also have faith in Yamadeva but this people have more faith to Shiva, so they will build Shiva temples, same with Rama, Vishnu etc.
Also worshiping Yamadeva does not mean Yamadev will send you to Swarga (paradise), he is DharmaRaja, he will only judge you on behalf of your Karmas.
All gods have equal nature for all. yes your worships may bring you something, but worship itself is a satvika karma, so obviously you will get fruit for it.
Yes if you do Tapa of Yamdeva, and do Satvik Karma, he or any deity will give you boon. but to do so you have to accept Satva and leave Tamas, that you do with performing Tapa. Then and only you can get Boon or paradise or something you want from GODs. Everything is Karma only.
Having less temples does not mean the deity is less worshiped, in rituals whoever deity is required people call them in Yajna.
Today's india is a fraction of what its spread was even a thousand years back. Yama was the main god in modern Afghanistan and Iran before islamisation. Till as late as 1890s, he was the main deity of the people of kafiristan in northern Afghanistan. The Persian Zoroastrian religion is partly based on Yama Raja religion.