The simplicity of it is logic defying. It used to be that you had to find crosswalks or move puzzle pieces or type blurred letters and numbers, but NOW all the sudden I can just click a box and HEY!, I’m human?
That’s hardly the Turing Test I’d expected.
some of them are also less bot detection and more spam limiting and mitigation. cloudflare’s has more stuff built in I’m sure, but things like mCapcha are just proof of work, so if you’re trying to make a bunch of accounts or whatever, it’s really computationally expensive.