I'd actually argue that inXile being a smaller studio could be what makes it more attractive to him. Obsidian is still doing contract work to pay bills while they also do passion projects, which, while it doesn't necessarily mean that Avellone's own projects have been getting full on shot down (though likely), could very reasonably have created a situation where projects he wants to work on are getting sidelined in favor of Armored Warfare and their Pathfinder projects. inXile being a smaller outfit seems to be working out to where they aren't needing to take on contract work to pay the bills. Since they've also been shown to be capable of working on multiple projects at one time (albeit slightly staggered), it may be more appealing to him since it would maybe promise a lower waiting time until he gets to lead something.
Of course, I could see him just freelancing for a while. It might give him a chance to discover new ideas and stuff.