The problem is that Windows discourages hobby coders. If somebody is going to invest the hardware and money required to develop software on Windows, they need some kind of return on it. That's why you rarely see free Windows programs.
Compiling stuff on Windows takes a lot of set up and configuration, and is over all not fun. On Linux or Bsd or Unix, I cd into the plugins folder, and tyep "make <pluginname>.so", and it automatically compiled it. On Windows, I'm not sure what you have to do, but I have yet to figure it out.
So yeah, Windows is too difficult to compile software on.
As another example, from the xchat website:
Q. Why isn't the Windows version free?
A. Building X-Chat for Windows is a difficult process, it requires quite some skill and expertise to accomplish. It takes time, and is by no means automated.
There you have it