Except, that's most of its ad copy on Google's own website?
reCAPTCHA uses an advanced risk analysis engine and adaptive challenges to keep malicious software from engaging in abusive activities on your website. Meanwhile, legitimate users will be able to login, make purchases, view pages, or create accounts and fake users will be blocked.
It's literally billed as a security measure for a website.
I mean, except they do. Just because their simple ad copy omits it, doesn't mean that's not what they're implying. It's literally listed as one of their security products and also uses the term to talk about demos
https://cloud.google.com/security/products/recaptcha