There was a good reason to allow name changes. With this new enforcement Southwest is practically begging group leaders to book refundable tickets for the new passengers, use those tickets to pass TSA, then cancel those tickets (or not) and have the new passengers board using the paper boarding passes of the absentees. Such a reaction by group leaders could cost Southwest revenue by preventing sale of additional full-fare tickets.

I don't see how the new policy makes sense for Southwest. It will cost them money, not make money.