It is, but barely (windows is @ 61%, macOS is at 46% based on the numbers I found). And even if we ignore that, number of potential users is far from the only factor you’d consider when choosing the first platform to target for a new project. And then, ignoring that as well, just because an OS has more potential users in total, that doesn’t mean it has more potential users of your editor.

There’s lots of reasons to not choose windows as a first release platform, and it being ‘the most common development platform’ isn’t a compelling one, especially for a small team with finite resources.