If spam is the issue, then why not ban the website they're linking it to? Or, if they're doing it repeatedly, then just ban them altogether? No better way to keep the forum out of spammers than to filter and restrict their posts and/or ban them from the forum, right?
Probably because there are multiple new websites created daily which are then spammed here across unrelated threads.
I think it would be way more effort to ban each site, than to simply restrict newbies from posting URL's. But both is a good approach.
It would. I mean, filtering out some phrases should teach spammers a lesson. Just looking at the list of the websites OP shared, it would be helpful to ban that particular website, or at least certain phrases that they keep on using. They'll eventually find another way to spam, but that should keep the forum spam-free for a while.