Why is Unity the most popular engine?

I appologize for my words, I meas a lot of developer want to use unreal engine for mobiles, because unreal engine 4 is a good engine, so does Unity.
I think the users should push epic to make unreal engine better, slander Unity will not helper(some people here).

there are more mobile developers than PC and console, they want to join unreal engine 4 and make it better.