The presumptions there are not all…

The presumptions there are not all true in that captchas are unique to solving them:

Brute-force protection doesn’t require captchas to solve. IP throttling goes a long way, and botnets can be detected at scale too.

Form spam can be filtered by content filters instead.

Web scraping is the same deal as brute-force protection.

Fakes signup: if your user account is so highly valued, require phone number verification.

Web resources: again, rate limiting.

Sure captchas can help in those areas, but they are overly employed I think because they are a good business and those business keep pushing them as a solution for everything, and in turn create a bad internet user experience overral for how widespread they are now.