A big muscle memory use case for the title bar is to support a larger drag target for organizing desktop windows. Presently, if the web page’s title is long, the drag target area is limited to the small margin in the title bar (below the title text). It would make a lot of sense to allow the title text itself to also be part of the drag target.
Relatedly, the blank space in the vertical tab bar could also function as a window drag target space.