"OK, so we're going to do a Linux version. How are we going to get it into the hands of our customers? What, we need to set up a download infrastructure for that? No, that's way too much overhead for a Linux version. What, we're supposed to partner with a small niche digital distribution platform we've never heard about? No, not worth it, either. Wait, we can just upload the Linux version to Steam, where we already upload our Windows and Mac versions? Sure, why not."
As for distributing binary blobs: You're overstating the issue, IMHO. ABIs in Linux userland are fairly stable these days.