Exactly. It probably increases conversion because it looks secure.

Credit card forms are sometimes used that way too, they get a lot of extra information because if they don't, people feel that they're scammy.

But surely a working captcha would increase conversion as well and have the added benefit of being a captcha?

And you really have to wonder, because the last time I had to implement a CAPTCHA (around 5 years ago), it was about 5 minutes of work. Google query, found a library, downloaded the library, copied the example into a form, and I was done.

I can't imagine coming up with your own clever hacked-together bogus CAPTCHA would be simpler than that. So they actually did it the hard way?

That's a Douglass Adams quote, isn't it?