PocketPC/Mobile, in particular in the corporate world, was massive. And in the "consumer" world, HTC made a name for itself by making PocketPC based devices with a range of designs.

Come the Windows Phone 7 announcement, they also renamed the PocketPC lineage to Phone 6.5, but it was clear that Microsoft was barely keeping it on life support.

Thing was that Phone 7 could not run PocketPC lineage software, full stop.

This meant that all those corporate and consumer programs (Opera Mobile came to be on PocketPC a decade before Americans were all hot and bothered about web on a mobile devices) had to be rewritten anyways, so why not look for alternatives (like Android).