Delta/Bombardier might own them as an intermediary but they are really owned by a leasing company. The leasing companies have deserts full of these things and are willing to sell/lease/give them away at this point. It wouldn't surprise me if you started seeing some of these 50 seaters get sold right back to the regional that operated them after the mainline carrier gave up their rights to extending the lease. The engine maintenance and overhaul is where it gets tricky.