Delta does not own the aircraft. It’s a bit more complicated than just saying the NBA owns them but Delta is just leasing the airframes. The NBA payed for the reconfiguration and Delta can’t change the seating. Here is the legal explanation.

According to a letter obtained by Bloomberg from NBA attorneys to federal regulators, the new aircraft will join Delta’s current fleet of eight Airbus A319. The 11 Boeing aircraft will be transferred from Delta’s ownership to a private leasing company, which will then lease the aircraft to a trust controlled by the league. As part of the leasing agreement, Delta will have full rights to the aircraft, including use of the aircraft for other charters.