I have wondered that too, I don't like the look of the new taskbar, I was hoping they'd do more with it with some of the user concepts floating around (such as a rounded floating taskbar.) I'm sure the true reason is that is what MacOS does, so they just copied it.

With (ultra)widescreens these days moving the Start Menu and Search boxes to the center of the screen makes a lot of sense. Literally brings them "front and center", and I guess if the menus/windows/boxes are moving to the center, moving the icons that open them to the center makes sense.

As a vertical taskbar user (since way back in XP days) though, I'm definitely upset by all the wasted space. I'm perplexed why they aren't allowing vertical taskbars at launch. I'm sure telemetry suggests most users keep a bottom taskbar.