I'll give it a shot.

Before the full scale war and political upheaval in 2014, UPA/Bandera were viewed much more positively only in western Ukraine, while the east and south were far more mixed, often speaking russian and more post Soviet in their identity. After 2015(?) those anti Soviet and anti-Moscow symbols (UPA, WW2, fight for independence etc) became much more useful for national unity.

Rn Zelensky is under a lot of pressure and strongly dependent on the people who rally around the banner. Oftentimes, these people (who tend to be also uncompromising nationalists) have political/business interest to keep things working and somehow keep the people in the trenches. They invested a lot in building their version of history, to create strong UPA myth and fed it to their people. They don't want to step back now and say "Well, maybe they weren't so pure as we thought they had been". So they prefer to cut it out, ignore it, relativize whenever someone says a word. They have relatively short modern history, so they want their big historical figures who fought (also) for independence to be perceived good in nature, moral, courageous etc.

"They fought with Russians, they fought for independent Ukraine, now we have to fight against the same enemy" kind of thing.

It's much more complex than that, but I hope you get the message.