They are annoying but I don’t understand why they being used on a site would be correlated with usefulness. Pretty much any site that bad actors would want to spam or scrape would be incentivized to use them. (Whether they work or not is a separate question)

Big sites like Facebook and Reddit can avoid using them because they have teams dedicated to identifying bot accounts algorithmically. But anyways those aren’t working well so those platforms and their users are suffering as a result.

> I don’t understand why they being used on a site would be correlated with usefulness.

Simply from personal experience. The majority of the time when I hit a captcha or somesuch, it's been for websites of marginal usefulness to me.

It's certainly not some sort of hard and fast rule -- there are plenty of exceptions as you point out. That's why I consider it a weak signal. But if other weak signals make me doubt the site is useful and I hit a captcha, I'll just move on immediately rather then continuing to spend time checking it out.

I think it's mostly that doing a captcha is a cost to me in time and irritation, and if I don't think the website is worth paying that cost, I won't.