While there is a lot I don't understand, I believe that corruption is necessary to win elections:

https://medium.com/politically-speaking/my-brush-with-political-corruption-5d8c4c255bc8

I think it would be naive to assume that anyone could have cleaned up the kleptocracy in Ukraine in one year. Political requires a balancing of many forces. Mr. Zelenskyy was making "some" inroads and that was upsetting some powerful players in the back rooms.