The major cost barrier is support. If you are going to sell a product for a platform, you need to be able to have your CS staff handle support tickets involving

The major cost barrier is support. If you are going to sell a product for a platform, you need to be able to have your CS staff handle support tickets involving it. Officially Steam on Linux only supports Ubuntu and SteamOS, so you can just throw out problems on other distros (albeit I'm not aware of any distro not taking responsibility for Steam breakages that work on Ubuntu and they aren't that common either). Even then, having to implement that support infrastructure is time consuming if you have never supported that platform before. It is the first game that is the hardest. That is why publishers like Paradox and 2K can just throw almost every new release on Linux nowadays since they are all made on portable engines, are going to support OSX anyway, and they already have the support infrastructure for SteamOS and Ubuntu. Its not even really an option, either. Since the games are commercial products in many (European) countries they have to by law support them in this way.