Half of the commits are from single person, and if he doesn't have or strongly care about Windows, the support just wouldn't be there to maintain it.
That doesn't mean you are forbidden to try it ;)
I have to admit, last I wanted to have IHaskell on windows, I just ran it in docker :-)
That said, I am happy to help folks get it working natively under Windows. There is a somewhat challenging technical issue, which is that IHaskell uses the Haskell `unix` package, because it needs supports for creating and using pipes in order to intercept stdin, stderr, and stdout. I'm sure that this is somehow also doable on Windows, but it just takes someone who wants to dive in and get it working; I'd be happy to advise such a person and merge any changes they need to make.
So far the entry barrier was too high for me but I want to reach out and ask if anyone is willing to hold my hand a little so that I might get over the initial hurdles. Could you suggest some entry points for me? A bug tracker, an IRC channel, a github issues page? Should I just hack on it on my own until I have a specific unit of work to contribute, or is there someone who could use my help with the coding and provide guidance as to the organizational side of things?