Why don't our Gods and Goddesses prevent Kali Yuga from happening?

Question

Nothing to add here, but it is mandatory, so...

Answer 1

Why don't our Gods and Goddesses prevent Kali Yuga from happening?

Because it's part of the plan and leela of Brahman, and the adharma in kali yuga is actually sanctioned and brought about by Brahman. This is all part of Brahman's leela (divine play). The yugas of satya, treta, dwapara, and kali all arrive and disappear at specific times managed and coordinated by Brahman.

Kaushitaki Upanishad - For he, Brahman, makes him, a soul, whom he wishes to lead up from these worlds, do a good deed; and the same makes him, whom he wishes to lead down from these worlds, do a bad deed.

Your question can really be reduced to, "Why does God allow bad things to happen?". And one answer is given in the Bhagavata Purana:

7.1.8 - When the sattvaguna is prominent, the rishis and devatas flourish with the help of that quality, with which they are infused and surcharged by Brahman. Similarly, when rajoguna is prominent the asuras flourish, and when tamoguna is prominent the Yakṣas and Rākṣasas flourish. Brahman is present in everyone’s heart, fostering the reactions of sattva-guṇa, rajo-guṇa and tamo-guṇa.

So good and bad actions are actually caused by the Lord, in accordance with the free will of Jivas. In Kali yuga, the Lord Brahman causes the adharma of humans according to their free will.

Answer 2

Ishvara (Krishna or brahman ) has created his own divine Leela and Lord Kalki, incarnation of Lord Vishnu (or Krishna ) will come at the end of Kali Yuga.

ŚB 12.2.19-20

अश्वमाशुगमारुह्य देवदत्तं जगत्पति: । असिनासाधुदमनमष्टैश्वर्यगुणान्वित: ॥ १९ ॥ विचरन्नाशुना क्षौण्यां हयेनाप्रतिमद्युति: । नृपलिङ्गच्छदो दस्यून्कोटिशो निहनिष्यति ॥ २० ॥

Lord Kalki, the Lord of the universe, will mount His swift horse Devadatta and, sword in hand, travel over the earth exhibiting His eight mystic opulences and eight special qualities of Godhead. Displaying His unequaled effulgence and riding with great speed, He will kill by the millions those thieves who have dared dress as kings.

So, God descends at end of Kali Yuga to annihilation of miscreants to maintain the universe

ŚB 12.2.23 यदावतीर्णो भगवान् कल्किर्धर्मपतिर्हरि: । कृतं भविष्यति तदा प्रजासूतिश्च सात्त्विकी ॥ २३ ॥

When the Supreme Lord has appeared on earth as Kalki, the maintainer of religion, Satya-yuga will begin, and human society will bring forth progeny in the mode of goodness.

Also, Krishna has said in Bhagavad Gita that he descends every Yuga to protect the pious and annihilate the miscreants

Bhagavad Gita: Chapter 4, Verse 7 यदा यदा हि धर्मस्य ग्लानिर्भवति भारत | अभ्युत्थानमधर्मस्य तदात्मानं सृजाम्यहम् || 7||

BG 4.7: Whenever there is a decline in righteousness and an increase in unrighteousness, O Arjun, at that time I manifest Myself on earth.

Bhagavad Gita: Chapter 4, Verse 8 परित्राणाय साधूनां विनाशाय च दुष्कृताम् | धर्मसंस्थापनार्थाय सम्भवामि युगे युगे || 8||

BG 4.8: To protect the righteous, to annihilate the wicked, and to reestablish the principles of dharma I appear on this earth, age after age.