actually this is another one you can blame on SCOTUS, but it was the Burger court. Ruled in 1978 that states could not prevent nationally chartered banks from charging higher rates than a state allowed by its own regs. Before that a lot of states had pretty reasonable caps. The problem in that era was that inflation was taking off, making the locally legislated caps a loser for the banks. And of course in 1978 credit cards didn't have nearly the market penetration they do now.
This is why if they do something it should be more nuanced than a simple caps on rates. If you cap them at say 10% and inflation goes about 7% no bank is going to offer you credit at that low a return and suddenly you have a big drag on the economy, If you cap the rate so high that the business/inflation cycle is never a problem, it's probably too high to give consumers any serious relief.