I don't understand about the popularity of Lord Shri Krishna, even though he cheats in Mahabharata for Arjuna's victory and even though he had thousands of wives, he is considered true symbol of love, still he didn't marry his true Love Radha?
The answer indeed is Shri Krishna's leela (pastimes) as stated in the comment by Kedarnath above. There is no other incarnation of God where so much leela manifested as it did in the avatar of Krishna. Starting from His birth till His disappearance from earth, all His activities were full of play and turn of events. His human like activities of stealing butter, telling lies, etc. create affection and devotional feelings and it becomes easier to think about Him more and more. Hence, Shri Krishna is also known as Leela Purushottama.
Now it's true that cheating in the war is certainly not a likable activity, but He did it for the purpose of establishing dharma by defeating the adharmi Kauravas through the hands of Arjuna and other Pandavas.
Regarding marrying thousands of wives, He did it because those girls were under the captive of a demon named Naraka. When Shri Krishna killed the demon, they all accepted Shri Krishna as their husband (SB - 10.59.34). And regarding Shri Krishna not marrying Radha, it was due to the effect of a curse given to Radha by Shridama. Please see this answer regarding this curse.
Like I said in comment Leela is the single word answer for your question.
Coming to practical life, We have three main God , Bramha, Vishnu & Mahesh.
- Brahma ==> Creator of the world
- Vishnu ==> Care taker of life & all jivatmas
- Mahesh ==> Destroyer of the world
When the brahma creates the world, his work is over and Lord Vishnu comes in the picture. It is his duty to keep running the world properly with Dharma. Due to this he keeps taking avatars.
When brahma creates the world we ( humans ) doesn't know much about the worldism/jivatma. We only knows Vishnu & his avatara's as it happens during our life time. When the world's time is over Mahesh takes his action.
So conclusion is Vishnu's avatars & Leela is the only stories we heard most during our life time, This is the one of the practical reason as per my point.
In reality each God has same importance but during creation & destruction we are not much involve that's why we think that Vishnu has more attraction, but I don't think it is.