it is a weird dance, for sure. But currently, they're very dependent on Windows (and based on the restructuring at Microsoft, dependent on Windows remaining a big thing indefinitely).

While saying Linux First outright is probably a bad move, they do need to funnel developers' attention elsewhere to something either they control (a linux distro called SteamOS) or something compliant with Linux in general so that whatever flavor of the month distro can run them. I'd personally aim for the latter as it enables sales to people in love with Arch, Ubuntu, etc., but I could see a push for SteamOS too.

But yeah, Linux only? Not a good idea. Creating incentives for companies to target Linux too seems like a good path, but at the same time, you have to make it worth their time to support another version.