Star Wars: The Old Republic? BioWare scribe Alexander Freed says it has to do with both development costs and a concept called relatability.
"There are enormous technical obstacles, there is building all the lip synching, all the emotion into the face of the human is incredibly difficult and time consuming, doing that for something like a Wookiee –- and we couldn't half do it, we couldn't let Wookiees be only a third as expressive as humans," Freed explains in an interview at VideoGamer.com. He also touches on the fact that BioWare (and Star Wars) stories have traditionally revolved around human characters due to the ease with which most gamers relate to more familiar avatars.
Freed also mentions TOR's grand scope, and opines that other companies looking to follow BioWare's lead may have a rough time. "Even we didn't know what we were getting into at the start. I think it will be difficult for people to attempt it the same way. I kind of hope they do -- it will be interesting to see," he says.
[Thanks to Emily for the tip!]