Because one would think that it would be in CloudFlare's interest not to harbour criminals on their network. This logic seems to work almost everywhere else on the internet, including privacy friendly hosters in iceland. It's mostly just CloudFlare who replies to every abuse report with the same "WE R A REVERSE PROXY", no matter what the actual issue that was raised with them was.

If they were any smaller, their IP ranges would just go into the rogue-isp-blocklist, and that would be the end of that. But because they're mixing in the criminals with their normal customers, that's not really possible.

And since I am unlikely to be in any jurisdiction that CloudFlare is in, nor do I have any chance of finding out who these criminals are because CloudFlare is protecting them, going to the police here wouldn't really achieve much.