I think the majority of fans know he's a talented runner but I disagree his fumble problem is overblown, coaches hate when RBs cough up the ball, because they will have trouble trusting the guy won't do it again next time/carry.
The problem that I have with BB is that he doesn't make the effort or show the wilingness to protect the ball. For instance, during a pre-season game he turns the corner to the right sideline, the DB is closing on him and hits him when he's still carrying the ball with his left hand/arm. This is basic stuff, you switch the ball to the other arm to protect it and to see if you can stiff arm the guy. He had time to do it but he never did on that play. Also he doesn't put the other arm around the ball when he's about to get hit, you see all RBs do this to protect the ball, at times he just doesn't
Maybe the coaches addressed this issues to no avail, maybe BB is hard headed about it and won't change his ways. I don't really know, but it's a shame because is a correctable thing.