Windows does this for top-level menus for the same reason.
Or at least it did in classic Win32 UI. You can still see this in action if you open, say, Disk Management. But in Win11 Notepad (which is modern XAML), holding mouse down will open the drop-down submenus, but you won't actually be able to activate an item by releasing the mouse button while hovering over it, so it seems that someone partially copied the design without understanding its purpose.
Or at least it did in classic Win32 UI. You can still see this in action if you open, say, Disk Management. But in Win11 Notepad (which is modern XAML), holding mouse down will open the drop-down submenus, but you won't actually be able to activate an item by releasing the mouse button while hovering over it, so it seems that someone partially copied the design without understanding its purpose.