It doesn't take a fan to potentially make a good game movie. It takes people who are willing to look into the history of the franchise, see the stories and characters, and be willing to use all of the mythos that franchise has to offer in building the script. From there, it takes people who are actually good at their craft... be it acting, directing, cinematography, whatever. And then of course, you need people who are good at special effects, set design and so forth.
The problem with game movies, is that most of the time there are several of those things missing. They might find decent actors, or get some nice shots, but the majority of what gets laid to film feels like everyone was slacking off... they it was just being done for a paycheck (i.e. anything by/for Uwe Boll).
There's nothing that says a fan will be good at writing, acting, directing, or any other aspect of making a film. Being a fan doesn't make that person skilled. You just need people who really care about their craft enough to be good at it, regardless of what the source of their movie is.