Some of it is that we simply don't have that much to go on yet. What will 5e really look like when it's done? Who knows. The Pathfinder beta play test was significantly different from the final PF core rules, for example, and 5e still has significant time until its official release.
The other thing I have to keep asking myself is, what is 5e going to supplant in my group's existing play set? We already have one GM running GURPS, I'm running Savage Worlds on the side as a diversion on our GURPS "off weeks"; we have a Pathfinder campaign on hiatus that I ran last year; I'm dying to get a full-blown Fantasy Craft campaign rolling.....
And no offence to WotC, but any brand loyalty I might have felt for the D&D name is looooooong gone out the 4e window.
Unless I'm 100% convinced that D&D Next is going to blow my existing options out of the water, why would our group change up what we're already doing?
So far, 5e looks like just another interesting d20 fantasy variant......and I've already got like, six of those.