1. It's landscape orientation. Shows up smaller in the MM scheme of avatars.
2. Complex background. Harder to 'read' image in a small thumbnail.
3. It's B&W. Color attracts attention. Black is NOT a color.
You have a lot of images that will serve as much better avatars. An avatar should attract viewers to your portfolio. Since Model Mayhem is a facility for networking with models, pick an image a model will respond to. I guess you are looking for male models who can float in the air based on your avatar. But I'll bet you really want attractive females with both feet on the ground...
Save that image for a gallery exhibition where you are showing off for other photographers.
As an image it's interesting, I would also like to know how it holds up as a print. As an avi it's not good, aside form the above reasons it doesn't project you or your work. Someone interested in it clicks, goes to your portfolio and sees what? Nothing like the avi that's for sure, so they need to match; change the avi or your book.