Yes, and Youtube and Facebook both have similar problems. There is survivalship bias at play here, you do see the bots that manage to get past the spam protection, but never see the ones that don't. For all you know, Twitter could be blocking 99% of the spam. Of course, as long as there's money in it (and there is), spammers will constantly be coming up with new and unexpected ways to bypass your systems. It's a neverending battle, and if you think it's trivial, you are the one understating how hard the problem is.

I never claimed Tesla self-driving wasn't an achievement, but clearly they underestimated how hard that would be themselves, so I wouldn't be surprised if they'd do the same for content moderation.