Captchas are often used as tarpits. They've already decided you're a bot based on other factors so you aren't getting in until you change those factors. I've seen this happen where I'm stuck in the loop and then change the VPN endpoint and get right in after one try.
I'm sure there exist examples where people maliciously give tasks (captchas) out that have no chance of getting the person anywhere, but it's definitely not common
Consider yourself lucky. I routinely run into tarpit Google reCAPTCHAs and I don't even use a VPN. I think it's because I run Linux and the site admins treat anything besides Windows, Mac, iOS, or Android Chrome as suspicious enough to blacklist. It has gotten to a point that I literally never even _try_ to do image-based CAPTCHAs anymore. If I can't access the site, oh well.
I also get infinite captchas but it's imo not a tarpit if it's not intentional but a bug
Edit: looked up the term, DDG shows a Wikipedia card saying "A tarpit is a service on a computer system that purposely delays incoming connections." (purposeful)
It may seem purposeful on Google's part but I bet that if we could get through to the developers for answers, it's probably not designed that way but we're running into a case where the system isn't designed to handle it
Which could be said to be intentional (excluding people with our FOSS setup), I guess
