Yeah, because there are a lot of mechanisms by which a folder may start to execute code when you open it outside of restricted mode. A large fraction of addons have something which could be used for this, for example. There isn't a general check that it can apply ahead of time for this.

(They could, with some breaking changes, maybe try to enforce a permissions system for the matrix of addons and folders, where it would ask for permission when an addon does actually try to run something, but this would result in a lot of permission requests for most repos)