Writing software that works on multiple operating systems is hard. Adobe Photoshop doesn’t run on Linux, and they have a lot more resources and developers than the darktable team.
The darktable team recently published a blog post giving their reasons for why there is no Windows version:
The answer has always been the same: because no one stepped up doing it. None of the passers-by requesting a Windows build actually took the initiative, just downloaded the source code and started the compilation. No one approached the development team with actual build errors and problems encountered during a compilation using MinGW or else on Windows. The only thing ever aired were requests for ready-made binaries.
As stated earlier here, the development of darktable is totally about one’s own initiative. This project (as many others) is not about ordering things and getting them delivered. It’s about starting things, participating and contributing. It’s about trying things out yourself. It’s FLOSS.
Read the whole thing here.