Here's my question: how can this rule not be repealed?
It can be repealed. Instantly. It's a political stunt.
And, even if HRC had won, I'm not sure that there would have really been any way for the federal government to force states to fund something.
The same way the Federal government forces the States to do a lot things, the power of the purse. The most notable example being how by threatening to withhold a small percentage of Federal highway funding, the Federal government forced the States to all raise the drinking age to 21.