Maybe this is because he has the looks of a leading man, but the versatility of a character actor. He's done both successfully and probably the reason people don't recognize him from role to role.
His most seen work has been with HBO, first playing Mikey Mantle in the wonderful baseball picture, 61, and most recently as Ray Drecker, the teacher turned prostitute in the little seen series, Hung. Both of these projects showcase his ability to be charming and likeable and one would think lead to more high profile projects.
He is most likely enjoying the work without the celebrity, but Thomas Jane can't hide forever. He has all of the right ingredients to become a full-fledged star and once he lands that big box office hit - look out.