The spammers are taking advantage of open fediverse instances - and it’s not one, but instances chosen at random. You may think that banning instances would solve it, but it will block other legit users.
Some of the automod bots are also filtering and blocking posts based on the content as well (RegEx, confidence rating based on the age of the account and upvote/downvote ratio, presence of rarely seen domains in URLs), so that helps a bit.
The spammers are taking advantage of open fediverse instances - and it’s not one, but instances chosen at random. You may think that banning instances would solve it, but it will block other legit users.
Lemmy cannot solve the spam issue sadly, this not something the devlopers who built it think about.
Even if mods blocked every instance that has spam, as more instances become avaliable, it would be easy to spam or troll lemmy.
Some of the automod bots are also filtering and blocking posts based on the content as well (RegEx, confidence rating based on the age of the account and upvote/downvote ratio, presence of rarely seen domains in URLs), so that helps a bit.