Because many of us get the same puzzles over and over with reCaptcha, and often get sent into the infinite puzzles zone despite being both a human and answering correctly. The assumptions built in to reCaptcha just aren't good. There are people that don't accept cookies for anything, but who aren't bots. There are real humans using text-only browsers. There are people who's mouse and keyboard events fall far outside the expected range of normal human users, or who use aids such as macro keys that playback canned responses and confuse Google's methods. So I can definitely imagine anyone who's dealt with that shit for years being happy to have something different to try. Even if it's just as annoying, at least it's not the same damn thing!
My favourite failure mode was when I was using a roller as a mouse and it constantly failed. It took me a while to figure out that it was probably failing because my mouse would move in a straight line.
Naturally if I was logged into my google account I wouldn't have much of an issue, because I would be feeding the surveillance machine.
