At the moment, if you have no favourite sources/libraries, you get a very silly looking first-load experience:
So every time the page loads I need to manually click “More” to show all my libraries. I don’t want to have to manually sync all my libraries with my favourites, that is laborious and silly when a simple if statement might fix it.
If I reset and it auto-pinned everything, if I later added a new library I’d still need to manually add it to my pinned libraries right? If so, I still think improving the default behaviour is better than forcing the (admiteddly minor, but annoying!) maintenance burden onto the user.