That doesn't mean it's automatically how things should be. The Supreme Court doesn't rule on that. If the Supreme Court was the only measure of "correctness", then the US might as well wipe its statute book clean.
Another way of looking at it is that the Supreme Court has only ruled that they aren't _un_constitutional. It's then up to Congress to decide whether or not they should be illegal.
I read elsewhere on this page that apparently the Republicans blocked such things from becoming illegal.
In my view as a non-American, it feels like Americans attribute too much weight on things they don't like on the Supreme Court, which deflects from the reality that it is the major political parties (perhaps just one) supporting this status quo.
The Supreme Court isn't an unquestionable authority on what is right. They are our pragmatic system of determining what our laws (including the constitution) actually mean in a given context. Sometimes they do great at that. Sometimes they do terribly. We don't all agree on which is which! Even when they rule on something (rightly or wrongly), the law can be changed afterward to undo the effects of their ruling (even the constitution). In this case, many (including me) would argue that that was a terrible ruling and that laws should be passed to clarify that you can't sign away your right to a trial preemptively.
