The supreme court literally decides whether X real-world activity is made illegal by Y law. Interpreting the rules is making rules.
This doesn't seem to be such a problem in other countries. I don't really understand if that's because the judges are purposely appointed to be as partisan as possible, or whether the 'rules' are so badly written that they can be interpreted any way you like.
It's a philosophical difference in legal systems derived from the Napoleonic code (and more indirectly the Roman legal system, so it's common in continental Europe) vs. the English legal system (the US, Canada, India, Australia, etc)
https://en.wikipedia.org/wiki/Common_law#Common_law_legal_sy...
And to your second point, the popular vote went Democratic in the last 7 of 9 elections (and electoral in 5 of 9) but 3 of 9 Supreme Court Justices are Democrat appointed. The court does not reflect our deeply ingrained values.