Bennett's value would probably be pretty meager, considering how key a role he plays on a team gearing up for its title defense in a few months.
You could certainly find contenders willing to add him in exchange for good futures - a first rounder and a decent prospect, maybe. Yet do futures move the needle for the Panthers? They would ideally want to replace him with a comparable veteran playing a similar role, with similar size, snarl, grit and production in him. Contenders won't be offering that.
And neither will Florida.
If a contender has a player it can't sign under its payroll/budget, it keeps him for the playoff run and then looks to replace him in free agency. Teams in Florida's position don't prioritize asset management. If anything, they trade for more players they know they won't keep beyond June.