Pro AMA (AFT) restricts the number of teams to 16. They have running qualifications to develop row placements in the semis. Removing the heats seems to serve 2 purposes. 1) Less expense for the teams/privateers because of wear and tear, 2) it takes less time to run the event.
With the limited entries, heats are unnecessary. EVERYBODY makes the main.
AFT's goal for years has been live TV. That requires a predicable time window. The big question nobody wants to talk about is whether there will be anyone still interested in watching or anybody who can afford to run when AFT finally secures a contract. Yeah, that's over dramatic but not by much.