If these were tabs in Preferences they would all 4 be totally empty in new browser.
I agree. And I personally don't have a problem with it.
what is the use case for this?
Everything can be accessed from one place and using one shortcut.
I mostly need the password and extension tab within preferences window (since Safari also ships as such, I am used to this, and maybe others are too).
History and Bookmarks have their own menu bar. So they can be accessed directly (and so, maybe they can be kept separate from consolidated window). But for extensions and especially passwords, it is a bit cumbersome.