The issue is that they're not commonly used, and even if that changes, the ISPs can roll out harder-to-bypass censorship methods like SNI inspection or IP blocks.
You can't win the war against corporate censorship and malicious anti-freedom politicians through purely technical means. But you can sure make it much harder for them.
Oh but they can, we are suffering this in Spain every weekend the football league plays.
Tons of Cloudflare IPs sent to a blackhole regardless of how many other non relevant websites are behind.
Some business are really angry because they claim their peak hour of the week is during the matches (e.g. wife buying online while husband watch the match)
And they don't deny doing it, they claim they block Cloudflare because they host piracy, child pornography (how would they know, did they search for it specifically?) and other illegal stuff and their response is basically "complain to Cloudflare" or "those blocks affect only 4 nerds [using Github, Cloudflare tunnels, Docker Hub...] so we aren't going to change anything".