TLDR: drugs in a nutshell.

Its because we don't know what effects a drug will have until we actually inject it. You have to realize that our entire body is a diffusion prone liquid chamber of a billion moving parts but we need to deliver soluble drugs to a very specific target number of cogs. That's physically impossible btw.

So we end up having unknown side effects, and every drug has them. We just have to be persistent and select the ones that are effective at curing yet tolerable enough, but this process can take upwards to a decade in clinical trials.

In practice this means we have a decade long backlog of drugs that we think are promising but haven't had the time or resources to check. We'll get to testing CRISPR in maybe a few more years.

One more thing, as a scientist who has used CRISPR systems in cell cultures, its not that 'robust' yet. If I had to choose between successful CRISPR and fliiping a coin in a game of russian roulette, I'd still take the coin lol.