Most people just don't think about collaboration issues enough to understand what they're losing by not upgrading from email. They just, 'we have email; we have what we need'.
when I look at my Google Wave page I see dozens of people all typing to me in real time. I don’t know where to look and keeping up with this real time noise is less like email, which is like tennis (hit one ball at a time) and more like dodging a machine gun of tennis balls. Much more mentally challenging. - source: http://scobleizer.com/2009/10/01/google-wave-crashes-on-beach-of-overhype/
It is noisy, but the noise often happens way down in a wave deep in your inbox.This is far far worse than email. (New email always shows up at the top of my inbox, where Google Wave can bring me new stuff deep down at the bottom of my inbox). - source: http://scobleizer.com/2009/10/01/google-wave-crashes-on-beach-of-overhype/
The interface is not confusing, it's just novel. Early adopters will use it, get it, and rave about it, and then other people will follow because they feel like they're missing out. And then people will nag their mums to get it so they can share pictures better. And then everyone will have it.
It's true that many organizations will think 'we have email, why do we need this?' but then other organizations will understand the benefits and adopt it across their organizations. Then business pundits will comments about the difference it's making and late adopters will feel the need to get it as well. I'm sure that, back in the day, most people didn't see the need for computers.
Too busy! Too much clutter! Not very google-like!