can anyone explain this to me please???

Can someone please explain to me why riot keeps changing the champions that people play the most and like instead of trying to ' bring back to life ' the ones the are not being played???. So noone plays urgot, noone plays galio, nooneplays zac, noone plays evelyn, noone plays quinn and the list goes on and on and on. Then there are the champions that are being played less and less.

Now riot instead of trying to make changes to these champions so that they start getting picked again, they keep messing with champions like kassadin, katarina, tristana ect....

Why is this happening, why would you have so many champion thrown in the trash can while all the ones who people like keep getting nerfed and keep being changed???