I think it's worth pointing out that this is about an article and a Reddit discussion posted literally yesterday. A fork might already have been on the way. Maybe someone was working in a private repo. It's clearly a worse solution than fixing the original so even assuming someone was willing to maintain a fork, it's not surprising that they wouldn't do so at the first sign of trouble.

If you do look at comments by safety-focused developers from earlier actix drama, you'll see that quite a few simply use a different project. The answer might be that actix doesn't provide enough value compared to alternatives to be worth forking for those people. The people aggressively attacking actix might not even be interested in the project for their own use, but merely there for the outrage.