Not saying there's anything wrong with catering to "comic fans" but commercially, the masses are a larger segment, and sometimes "simplifying" things helps you streamline a storyline and concentrate really on the important bits.
It's not that JL is a horrible movie per se, but we've been bombarded with superhero movies for the past half a decade so we've seen good, we've seen great, and we've also reached a certain saturation point too. We need more than to just see Superman or Iron Man flying through the sky to be "wowed" at this point. That might have worked if we were in 2007 and it was the first live action superhero movie generation, but now we expect more.
IMO if JL had come out around the time of the first Marvel Avengers, I think it would have performed much better, but we're a bit past that point.