I have no idea about the why, but I've seen the same thing. All new accounts spamming content to all of those (and at least one known-good user posting links there; maybe thought they were legit?). I've banned/removed them all locally on my instance, and I think some other admins are doing similarly.
All of those, if you go to their base URL, seem to be part of the same campaign (spampaign?): The Freedom Project / The Freedom Estate Project
I may just start blanket-banning *.pages.dev
for now and deal with any false positives case-by-case.