Here's some reasons:
- Sintim is athletically limited.
- Sintim has stiff hips and appears to have limited ball skills and coverage ability.
- Sinitm has experience but his ceiling is probably not very high.
- 3-4 OLB experience may not necessarily mean that Sintim won't have a big learning curve with BB's playbook and complex schemes.
- Sintim may be better suited to 3-4 SILB where he will have to learn a new position anyway.
Monty Beisel and Victor Hobson are good examples of athletically limited players who just didn't have what it took to play in the Pats' system. I don't see Sintim ever being more than a solid player at best. Barwin could potentially be a pro bowl player in a few years.