Ent said it was due to an augment virus. The TMP bumps don't line up with TUC and the significant variations of phenotypes.
Plus, TMP had no explanation for decades.
Discovery may have been a change but it was as extreme as TMP from TOS. The explanation is a catch all band aid.
Bumps are bumps. TMP was the first to show them. But it's established onscreen that bumps are unique. Like hair color on humans. But sticking 2 extra nostrils and making their heads more elongated is a major physical change. Sure there was no explanation for a long time. We all know what Roddenberry intended. There was zero need for another redesign. Enterprise and DS9 offered a fun explanation. I was good with it.