I think it has a lot to do with the load he's already carrying with pounding the rock so much. We don't have someone to give him a breather like we had last year with Tate. Maybe when Tate comes back from his injury, and is back up to speed, then hopefully the passes to Foster will pick up.
There's no doubt that he's dangerous when given the ball in space, but add another 40-50 yards of receiving to his work load and he's going to feel that even more. He's a great weapon, but we have to be smart with him. I don't think this is one of those "ride him til' the wheels fall off" scenarios. If that happens, then we are majorly screwed. He may not be putting up numbers that fantasy players want, but we're winning as a team. It may not always be pretty, but I'll take that W over him blowing out the stat sheets and ending up with a loss. JMHO.....
Edit: IIRC, I think he was averaging around 11 yards per reception last year. That's a remarkable number. I also think he led the league among RBs.
If it is important to you, you will find a way. If not, you'll find an excuse.