So why did they make taskbar bottom only in the first place? Too difficult to implement? Branding? No room for ads when it's vertical?
Someone correct me if I'm wrong cause I don't recall where I got this understanding from, but I believe Windows 11 still has the Windows 10 taskbar, but a startup process basically hides it and replaces it with a brand new one they made for Windows 11, built with web technologies. And they probably just never got around to figuring out how to put it somewhere else on the screen since they didn't inherit that behaviour from before.
Performance. They couldn't even handle seconds in the clock on win11 release.
Because the Apple dock is bottom-only too, and the Microsoft UI designers are using Macs.