Well, I pretty much joined this forum to ask, but I noticed that most (if not all [It's been a month or two since I checked]) of the fan games that you have for download here are PC only, something which bugs the hell out of me. Is there any particular reason, or is it just that a majority of people use PC's and the creators didn't feel like porting? I would just like to know, thanks in advance.

I'm guessing because PC may be easier to work with and it's more popular.

It's usually an issue of porting, quite a few of the development programs and software that aren't straight up coding languages are difficult to port, and some aren't portable at all (like game maker.) I know it's annoying, but there's not a whole lot the creator can do if their development program doesn't allow porting.

The thing that has made most Metroid games is a program called Game Maker, which is supposed to be coming out for the Mac (It was due months ago, but the developers keeping "not noticing" the deadline)
However, other things, like C++, the developer may not have a Mac to compile the (.dmg, I think?) game on, or even the libraries (like DirectX) aren't cross-platform. That, and its very hard to test a game in an OS you don't have. My friend has a Mac, I could compile my upcoming game on it, and I will for major versions, but I can't do it for every single version due to time constraints for testing and such.
Sadly, those Game Maker games don't even run in Wine, so you have no way of running them without a copy of Windows.