Question on Hope.

I am writing a fantasy novel that takes heavy inspiration from Lord Krishna's role in the universe. So, from what I know of Krishna, he says this quote Yada Yada hi dharmasya.... Sambhavami yuge yuge. But why exactly does he keep coming back? It is to destroy evil and establish dharma. What has he to do with this world which always goes towards evil? He explains in the mahabharata that he has belief in time and goodwill. Even I believe but I can't control the alternative thought. Because I have also learnt of other ideas within Hindu and Jain philosophies that the world can't be changed. Only you can change. So, why does Krishna try to change the world? He is already perfect and that's enough. The best possible explanation I can give is that while you are developing yourself intrinsically, why would you not try to uplift those around you for the time that you are here. You clearly have potential and therefore why not use it to benefit people, if that makes you happier. The utopia that we strive to achieve, even if theoretically possible, is impossible (implied) because of the yugas. If rise and fall is inevitable, why play a role in it at all? So logically trying to be free from the cycle of time, life and death is the main philosophy. So does Krishna do it all because of love? I know that mere attraction is not love, and Krishna says it too. But is love love, an attachment to this world, as Krishna keeps coming back to establish dharma? Is it to keep a balance between good and evil? And why does it matter to Krishna, if he is independent of time and the physical world?