How do you suppose they obtain the data to know how humans fare?

Sure, it's great for training/testing their AIs. But if the result is AIs better than humans at the task then it doesn't make a great captcha anymore.

Maybe they actually don't care about the captcha aspect - they just found a good mechanism to easily acquire data from humans that no one will complain about because it's so entrenched.

It still protects against spammers that cannot deploy such AI. Which is probably very close to all of them.

Hence the fancy "click if not a robot" captcha. :)