Many IPs are shared by more than one endpoint, and hundreds or thousands of endpoints sometimes share a single IP. Say a home router is compromised on an ISP using CGNAT and you block by IP, you could potentially be blocking an entire neighborhood of innocent users.

Having parts of the Internet blocked for huge numbers of their customers puts pressure on ISPs to monitor and censor users traffic, which is not the direction I want to see the Internet go.

IPs do not have a one-to-one relationship with users, and I feel strongly that they shouldn't be treated as if they do.