I mean one look at the website kind of tells you why.

The extension could be a lot less intrusive as well - just compare it to uBlock Origin for example. There doesn't need to be an onboarding message. I don't need to see "F.B. Purity hid:" prominently in the middle of my feed - just put that at the bottom right of the screen in gray text or in the extension. Etc.

I'm probably going to uninstall it because it makes FB even uglier.