[mechEpleb]

It boils down to the fact that there are large potential (if improbable) downsides to messing with DNA, and people have a strong cognitive bias against actively inflicting harm vis a vis just allowing harm to happen on its own.

I personally don't think it's possible to prevent this kind of thing in the long term, so everything ranging from edited children born with horrible disabilities to deleting some potentially beneficial mutation paths in the human genome from existence is going to happen anyway.