From reading between the lines of what Taylor has said, it seems like the new ones get played because IHeartRadio would prefer to keep Taylor happy than some skeevy music producer. Why would a major radio or streaming service want to alienate one of the most popular artists to save some money on streaming rights?
Also, a lot of Taylor’s fans are ride or die. I could see them actively choosing their streaming services or radio stations based on what version gets played by default.