Why is Perrines touches so inconsistant?

[impactplaya]

Fans may or may not like Sameje Perrine.
But everytime he touches the ball either
Run or pass, he averages 6 yds a touch.
The Jets 2nd RB Ty Johnson was a force
Vs the Bengals with 71 yds recieving and a TD

I don't understand the rationale of giving him
4 or 5 carries 1 week then the next week
0 carries.
Even in the passing game he has made some clutch
Plays then becomes a afterthought.
He is a surehanded target. Very consistent hands