The reason is that there are currently 20,000 parts in the library.

But to be clear I ment with the existing folders in the categories. Otherwise it would not be close to helpful. Don't know if they would still be to many parts to load at the same time

I would never load all the root components at once. It would kill the server. You can see that at the moment it only loads a maximum of x elements and if the parent contains more, you have to click the + button.

true. Because the + button changes its position all the time its probably a bit annoying when scrolling thou all parts. Its fine for the few folders where its needed, but having an "all" folder like that, probably wont improve that much