Google still has to routinely invent new techniques to stop spam. This problem is not solved - it's an ongoing arms race.
It is also a vastly easier problem - spam filters at google scale work because they see the same spam across zillions of accounts. This is not the case for youtube, where a spammer provides them with far fewer samples, and those are across a much wider space.
These problems are barely related.
(In fact, I wonder who these spammers are targeting. Surely the average YT user is smart enough to recognize blatant spam?)
Some random dude built an anti youtube comment spam tool. Youtube could absolutely fix this problem, they just don't care
5.7 - restricted terms
8.0 - username looks like base64
Gmail has the worst spam filter of any email provider I use today, excluding the one email server I have running on my domain that gets almost no email and has no filter. Or, well, spam filtering is a lesser problem on my server too because it doesn't block nearly all the email that I care about.
80-90% of the emails in my "Spam" folder are not spam.
It's worse than no filtering at all, since I still get exposed to the spam, but now I have to check two inboxes instead of just one, and then jump through annoying hoops to view images or access links in the second one.
For the company that loves encouraging obnoxious Captcha's to self-fund their AI/ML research and data harvest the web, they surely don't seem to like using it on their own platforms.