The app may not be great, but it's pretty good, especially for the vast majority of users. From Google's perspective, I doubt it makes sense to add features that many of their users don't need and won't use.
I only need the "feature" that when it crashes, it should remember the route so as not to have to use (often missing) data connection in the middle of the trip. It's such a simple concept - save all routes for later recall, even if offline.
