I normally use a VPN to access the Internet. It's an ordinary consumer-grade VPN, and I use it for pretty innocuous things like watching the international versions of Netflix or avoiding being geographically-profiled and charged more when I book travel. The VPN itself, I'm sure, is being used for all sorts of naughty stuff: when I look it up in whatismyip, it comes up as VPN, "abuse detected", and "residential proxy detected". I expect to get blocked occasionally on it and just pause the VPN then.
What I found surprising is that pausing the VPN doesn't always clear the CAPTCHAs. The next request will also fail, sometimes. For a while I was wondering if I have a residential proxy on my network, but I went hunting with lsof and bandwidth monitoring and a list of all the open connections through my router, and it seems clear. Yet even with VPN disabled, I'll get CAPTCHAs from Google and Cloudflare.
I suspect they're using browser/TLS fingerprinting and then smearing the results of that across bad IPs. If you connect to them through a known-bad IP, they not only will CAPTCHA you, but they will record a fingerprint of any data they can. Then if you connect again with that fingerprint, regardless of the IP, they block that too.
Ironically, if you are actually malicious, you can get around this pretty easily. Because you'll know not to use a fingerprintable browser, or to rotate fingerprints. So you have one completely separate identity on a given IP (that is not yours), and if it gets blocked, you roll up another completely separate identity on a different IP. But this is too much work for an ordinary consumer who just wants to keep their IP private. So you end up with this excluded middle where the only rational strategies are to either do exactly what the website expects you to do (with no funny business, even if it's innocuous), or to go whole-hog as the aggressor where you're determined to skirt their policies no matter what, and if you're doing that you might as well amortize the effort by extracting everything of value you can from them.