The dev comments say a lot:

https://old.reddit.com/user/paintboth1234

No one helping the project ever said “uBO is living on a secluded isle”. It’s a public community FOSS project, for over a decade, monitored and contributed by every user and volunteer. Every site has been watching uBO for years. It’s not new. And yes, if users do nothing to help, either on helping uBO’s side or leaving the trash sites, and just give snarky comments instead, this will happen.

The message is clear to me; UBO devs are sick of a sick of a sea of users constantly complaining about imperfect Facebook blocking, who won’t contribute anything nor lift a finger to limit/adapt their own usage. They’re sick of slaving away fighting six-figure-salary Facebook devs, whose only job is to counter adblock, where UBO’s only compensation is more pretentious complaints.

It’s not a technical limitation, persay. It kinda a “Why are we doing this to ourselves? If you all want us to support Facebook, fine; we welcome PRs.”

Which is totally fair.

To me, it sounds like UBO could drop other overtly hostile sites, too. As they should.