Expanding a bit on some of the reasons others have given, in this case I think it was also an attempt to grandfather a few states where sports betting was legal

Expanding a bit on some of the reasons others have given, in this case I think it was also an attempt to grandfather a few states where sports betting was legal. There would have been obvious problems with banning sports betting in, e.g., every state but Nevada. But banning state legislatures from authorizing it (if it wasn't authorized already) seemed, perhaps, less problematic. The classic problematic rationale, that the court discusses in cases like Printz [1] is also dislocation of the political costs of enforcement away from federal officials onto state officials. [1] https://en.wikipedia.org/wiki/Printz_v._United_States https://en.wikipedia.org/wiki/Printz_v._United_States