That's not how Microsoft historically operates. Programs I wrote 20 years ago still work on Windows using ancient apis that they carry, because they care about backwards support. Whatever obscure msc or exe you ran in the 90s is still there, still runs, and still configures the OS. To this day you can check weird boxes deep in your disk config to put buggy behavior back into Windows, because it fixes a bug a single customer had decades ago.

My theory is simpler: it was too hard to add new features to the taskbar (like wide search bars and now text fields) when you had to think about a tall and a wide configuration. So they cut the tall way. Now they can cram all sorts of features into your taskbar.

It represents a shift in MS philosophy, closer to how Apple mandates progress in their OS.