It's a double-edged sword. Just because it doesn't work perfectly doesn't mean it doesn't work.

To a spammer, building something with the ability to break a captcha is more expensive than something that cannot, whether in terms of development time, or resource demands.

We saw with a few Lemmy instances that they're still good at protecting instances from bots and bot signups. Removing captchas entirely means erasing that barrier of entry that keeps a lot of bots out, and might cause more problems than it fixes.