It probably is
Otherwise why don't any of these fucking devs just fix it by coding a web of trust relay to let new users in for submitting a NIP-13 proof of work note?
Discussion
Good question... Next question.
Really tho you're askin the wrong person.
However NIP13 states "This proof can be used as a means of spam deterrence."
"Can" is the most interesting part here. Possibly it requires measures that clients or relays dont support or want to support because reasons?
Genuinely no idea