why do you assume he'd be good at TE or LB/S? does he have the hands to play TE? or the blocking ability? Does he have the instincts to play LB/S? maybe he could have been a pro caliber TE/LB/S if he had spent years refining the position in college and as a backup in the NFL, but at 26, he's way behind the curve compared to guys of comparable age who have spent the better part of a decade refining their skills to be a TE/LB/S. it's a slap in the face to any of those guys that everyone even assumes tebow would just be good at their positions without years of training.
on occasion there will be a guy that makes the NFL that didn't play college ball (gates and graham at TE are 2 examples, which is why i assume everyone thinks tebow could do it), but they are bigger than tebow and much better all around athletes than tebow. and even then, it took them a few years to learn the position and become elite threats. tebow would be 28 or so by the time he'd spend a few years refining his skills and learning the position, why would a franchise coddle him along with there's 21 and 22 year olds they could invest that time and effort into instead?