In many cases, they realized that hactivism isn't a great tool for activism. Most sincere attempts were ineffective because they were causing minor damage and not getting much attention or support. We don't like that the NSA's spying on us? Okay, let's knock out access to their website. Having succeeded at this, what do you get? Is the NSA unable to spy? No, they're not degraded at all. All you get is one news story which most people ignore. Similarly with pro-Russia groups that took out the public-facing websites of airports in Europe and the US, which didn't stop flights from taking off like clockwork, nor did they inconvenience most travelers who would use airline websites instead. People who did that three decades ago often determined that there were more effective and less risky things they could do instead. A physical and vocal protest will probably get as much if not more attention and it has the benefit of being legal if you're identified.
I can think of only a few hactivist groups that obtained real results. The Guacamaya group, for example, which specializes in obtaining access to private information of governments and publishing it, has gotten more sustained attention to things they are trying to promote. Most others are either government-backed or acting like they are, going for destructive campaigns intended to back up wars rather than activist campaigns designed to change behavior or get attention.