It was a long time ago this was added (maybe 5 years?), but I think the reasoning there was that since our code competency is editing code, opening it should make that work well. The expectation is that most users should trust almost all their windows, it's an edge case for most developers to open and browse unfamiliar codebases that could contain such attacks. It also affects not just code editing but things like workspace settings so the editor could work radically different when you trust it.
You make a good point about the cookie banner reflex, but you don't need to use accept all on those either.