Because it’s far far easier to make a text-generation machine generate text that has decades of how-to explanations on the Internet than to correctly work an internal editor API that changes often and isn’t as well-documented.
Especially if you want effective results.
Claude Copilot does seem a bit more lost on the interface side than other models, but then again all of them are. Only the baseline tier seems to have been fine tuned to the platform.
I replaced common grep with a semantic search wrapper for some projects. It was amusing. It has a response header that lets Claude know it is not using standard grep. Works fine. Have to out smart them ;)