To much money lost by owner to ever do relegation.
They want to reduce tanking, if a team is in the high lottery more then 2 straight years, they start getting a reduced amount of the shared revenue (but this does not effect the the players salary) every extra year they are there.
So the players on the team still get their money, the team and owner gets a reduced amount. (in fact, they can connect that reduction percentage to what the GM makes as well)