Quinn is simply a damn good pass rusher. He joined the 100 sack club last year with a monster effort, but more importantly than the high-variance sack stats, his pressures per year have been really consistent.
A divorce makes sense for both him and the Bears. Quinn doesn't want to waste his last good years on a tanking team, and Chicago would rather free up the cap space for their rebuild. But the logistics of moving him are going to be tough this time of year. Half the league has $10M or less in cap space remaining, so it's difficult to even find a team who can pay him what he wants.
I'd say Quinn's most likely suitors are
Packers ($16M free and contenders)
Buccaneers ($12M free and definitely SB contenders)
Colts ($16M free, not really contenders but they don't suck either).
Panthers ($26M free and in a win-or-else situation, they will pay him if no one else will).
Regardless, Dallas isn't one of those teams, and he's not coming here. We don't have the cap space to take on his deal, nor are we really in a position to give him a starting role. Not with what we've already invested in Armstrong and Sam Williams.