Short sighted? Games have been developed for windows first (or X-console-first) for going on 25 years. Seems like game developers have done OK with that strategy.

The fact that windows-only is a poor business decision isn't obvious to me.

The tech here isn't great, Unity is sort of the banner of a decent cross-platform engine for building on top of but it has it's issues... for a game like this my guess is that the graphical rendering is very closely coupled with the game logic in an effort to save cycles. Your game being unperformant out the gate is a death sentence, your game being only available on windows means <1% of your market is disappointed.

I wish games had better cross platform support, but the motivation just isn't there monetarily and these guys tend to be financially strained as is.

I'm guessing that your not an indie dev :)