For the same reason they wont execute anything on that Microsoft 2019 video in 6 years. They'll ride Office to their deathbed, which is coming into clear view. Nice run.
This is how I feel as well. For a while I thought that Windows RT might be their stepping stone into these waters as a sort of clean break from the burden of backwards compatibility of x86 windows, but alas, it seems as though enterprise rules now until 6 feet under.
