While I agree with the spirit of what you're saying (as a linux user myself) the problem is that we have to recognize that developers have limited bandwidth. Windows is also generating more revenue for them, so it is going to take priority.

Though for an indie game it probably isn't crazy to make the code open sourced and then put those users to work for you. That can really help reduce the burden. But of course opens you up for people stealing your software (which let's also be real, happens anyways).