It has to do with the fact that the country has been in a civil war [0] since he came into power after the "revolution of dignity", not only him, but literally Americans who were fast tracked Ukrainian citizenship [1] so they could act as minister.
But a whole lot of people in those East Ukrainian territories liked the old government, they voted for it, and they saw their votes burned in a revolution to be replaced with Americans and people sponsored by them.
Which prompted them to do the same in their parts of Ukraine, leading to the separatists territories and a low to high intensity civil war that has by now been lasting 8 years.
> And only power he got was that in autumn of 2014 his party got a fairly good numbers
In elections where the old party was not even allowed to be voted for anymore, consequently, those elections were boycotted in territories that voted for the old government.