I have a game on Steam, developed primarily on Linux, and providing a Linux build (in addition to Windows and Mac).

Linux makes up approximately 0.5% of my sales. (Mac is about 2%, and Windows is the other ~97%) And from conversations with other developers, these are pretty standard percentages. I make and offer a native Linux build because I wanted to do it, but the financials really aren’t there to justify it from a hard business perspective.

Proton really isn’t the thing that makes game developers choose not to make and support Linux builds of their games; it’s the lack of an audience (and often developers not knowing enough Linux to be able to provide support for it). My hope is that Proton can build up the audience, so that it starts making more financial sense for studios to serve that audience.