That was what I was thinking as well for quite a while.

Fact is, there are people on TMO that use Android (and you might even find some that want it ).
Having it imposed at work is probably a big part of those that switched, though there may be people that are not tech-savvy enough to find/revive/use those devices or yore that we covet here on TMO (after my N900s died on me, I had to resort to buying a BlackBerry... with BBOS, mind you... no full-fledged Android for me, no sir !)
You can't also dismiss the fact that nowadays people are very partial to social networks and the whole there's-an-app-for-everything lunacy, and those are harder (if at all possible) to achieve on our cherished devices of the golden age, while it's the bread-and-butter of Android and iOS.

Lastly, I'd surmise people just want to get their grubby hands on the Pro1 ASAP, OS notwithstanding