"Create Folder" is such an often-used action, that it could have a button in the main toolbar by default.
Do you have any evidence backing your claim that it's often used?
I agree with Gregor, based on observing non-technical users use computers for my entire life. I grew up in a community of writers and college professors in the humanities who were very early adopters of computers but were and are entirely non-technical. Creating new folders is indeed a very common action. for these folks.
I would still love to see that contextual sub-toolbar implemented, then we can add actions that make sense for the current context (current folder, selection, etc), instead of starting to clutter up the main toolbar :)
+1000, that would be a better place for this for sure. Then the main toolbar could have only items that apply to the scope of the whole app and not the active view.