Fan films are a curious thing. To an outsider they seem like a total waste of time. Why spend thousands of dollars making a short film using characters that you don't own the rights to? Why not put that same energy toward creating something new and original that you might actually be able to commercialize?
The answer is easy: fan filmmakers do it because they love these characters so much they don't care about the financial side of it. Sure, it would be nice if someone like Aaron Schonke, the director of Batman: Seeds of Arkham, is able to turn their not-for-profit work into a for-profit career, but the ultimate goal here is always to make something that like-minded geeks can have fun with it.
As for Seeds of Arkham, this is actually Schonke's continuing the Batman series he started with City of Scars. At under nine minutes, it's not nearly as long as the latter, but it does manage to make good use of the Batmobile while also playing around with Poison Ivy and Killer Croc. Sure, it doesn't hold a candle to Nolan's Dark Knight, but it's not trying to, either. There's a low-fi love to this that reminds of old school television Batman, and we tip our hat to that.