Stage Manager follows the same pattern as the other features Apple took too long to realize were already figured out on the Mac: make it arbitrarily different to be able to call it new. Just like the “changing cursor” for trackpad support on the iPad. But hey, I’ll take it I guess.
Unfortunately, in previous cases, these “justification” tweaks have resulted in a strictly worse experience IMO. The transforming cursor on the iPad is distracting and it can be weird how it disappears over icons (resulting in me losing track of it sometimes). The iPad Keyboard is more awkward than a real keyboard, top-heavy, and sold separately of course. I wouldn’t be surprised if the same is true of Stage Manager, although at least it’s on the Mac too so hopefully if it turns out to not be that great, it won’t be excused as “people not getting it” like all the weirdo undiscoverable gestures on the iPad.