You joke, but I honestly wonder if this period and projects didn't involve a bunch of Microsoft employees who got a little overexcited when they were told that they didn't need to maintain the insane, sometimes bug-for-bug, compatibility layers with 20-40 year old software that they had had to deal with their entire career there.

Must have felt incredibly liberating, and maybe they got a little too into the whole idea of "fresh start"(s).

See also Windows RT.