And even if your team is superstars now it doesn't mean it always will be. What happens a few years down the road when you now have a team 5 or 10 times the size with people of varying skillsets and areas of expertise. Now that guy with mostly Python or Ruby experience needs to make some changes to your JavaScript code with what little knowledge of the language they have. It's helpful to write things to be as idiomatic as possible in those cases.