I think a big part of it is a lack of a premiere phone on Sprint. This would definitely be it--something that no other carrier has. (For now)
The Pre was that, or it seemed that way for a little bit. Until it became apparent that the device wasn't going "viral" and its popularity just wasn't taking off.
My wife and I are two happy Pre owners. Both of us overclock, use Preware (her's is all themed out with hearts and pink goodness everywhere). Performance issues, battery life, etc... well, it's liveable, not perfect.
I still think webOS has the best solution for federating work+personal stuff. I have TWO EAS accounts (1 from my company, and 1 from the company we're partnered with), 1 gmail account (personal), 1 google apps account (side job), facebook, all syncing contacts and other meta data to the phone. I haven't done contact management since 06/06/09 and I'm very happy about that.
Yet, through it all... I'll dump all that webOS goodness any day of the week to get an android BEAST with a 4.3" screen, senseUI eye candy, 8mp camera AND 1.3 camera, etc. If Palm had a device lined up for a June launch with Sprint that featured a 1mhz superphone, I might rethink it. But for now, move aside fellas... at least 1 Evo has my name on it.