I don’t know about “The Perfect Game” in particular–it sounds like it would have an audience–but the basic reason is that the studio thinks no-body is going to pay money for it. It costs a lot to release a film to theaters, and it even costs something to release it as direct-to-video. If the studio does not think those costs will be paid back, it won’t release it.
I imagine there could also be a rights issue, especially with is small production. Somebody during production figures “Hey, it doesn’t matter if that song is playing in the background when we film this sequence” only to be told later that yes, it matters a great deal.
I will note that the page you linked to seemed to indicate some people had seen it, which suggests that is was released at some level.