I can't find a link, but I remember when Ted Ginn first came to the NFL, he mentioned that he would step out of bounds when given the chance because he wanted to have a long NFL career.
From a financial perspective, he probably looks at this way:
Option A: Avoid contact, catch a few passes, and spend 10 years in the NFL collecting 7 figure paychecks. After all, he ran a 4.28 in the 40, and was a 1st round draft pick. As long as he's not injured, some team will pick him up, on the hopes that he "breaks out".
Option B: Fight for yards, take the hits, be more aggressive & productive, but risk serious injury. His thinking is that if he blows out his knee, his NFL gravy train will come to an end.
I don't think his thinking is going to change. This is the way he is, and he's always going to play scared.