They say AI is advancing greatly but I'm not convinced, most bots will still be bound to automated scripts and google should be able to avoid that. I think they also want to avoid inconvenience as its a standardised system
I'm not convinced that anything as sophisticated as AI is required for reCAPTCHA, I've been told they break it with good old fashioned brute force. Even with that being the case it is still the best captcha available at the moment.