I think it's more malicious than that. They know I use privacy tools and can't be tracked -> they can't make money on me -> bully me into not using their service.
It may also be part of their anticompetitive war on other browsers. I get captchas constantly in a new default Firefox profile, but not in a new default chrome profile. Spoofing user agent to recent chrome agent in Firefox makes the captchas happen far less often for me.