You bring up a good point about the US Supreme Court. My limited understanding as a US citizen is that they are there to interpret laws, not make them. I don't know how well that works in practice so I'm willing to be swayed on that stance if someone with more legal experience can present compelling arguments.

Chief Justice Roberts brought this issue up on his dissent on the Obergefell vs Hodges case few years ago. The constitution never addresses the topic on the legality of gay marriage and thus the court should not be the vehicle for delivering that decision; that responsibility falls squarely upon the legislative branch.