The first reason is very simple: he is a great player. Quinn is coming off the best season of his career. In fact, he broke the single-season franchise sack record. He was still able to produce in a big way even though he was often time facing double teams blocking. He finished the season with 18,5 sacks, 17 tackles for loss, 4 forced fumbles and 22 other QB hits. What he has accomplished is even more impressive because he was on a losing team. When your team is down, you have way fewer pass-rush situations. The Bears were down on the scoreboard more than 65% of the season.
But, the biggest reason for me is plain is simple. It does not make sense financially. If Ryan Poles trade Quinn, he would only free up $4,425,000. The cap penalty would be over $12.7 million as well.
I get that the Bears would benefit greatly from acquiring a couple of extra draft picks, but trading away a player of Quinn's caliber is not the right move.