nostr has 40k users and is incredibly useless and boring today so there is no point in doing adhoc "solutions" for the current users
once nostr gets to 80k users (still small and useless) we'll probably be getting much more spam
now imagine 800k
or maybe you're incapable of imagining future possibilities
by the way, the old reply guy and girls from last year, and the spammer that used tons of emojis, those were all impossible to counter with word filters, they have only stopped because they decided to, they were not countered