The two films you have mentioned do not have as much of a limited appeal audience as you would think. That is why both played to general audiences across the country.
The titles of have two films have either the words "God" and "Heaven" in it. Those two words tend to appeal to people with religious ties/feelings and that is a rather large group.
Where as MGP, by title, sounds like a "biker movie" and unless you delve deeper (which most people don't) you would not see the entire focus.
People tend to select movies based on title, rating and word of mouth. That is why the movie, "Noah", was released to general audiences and had a better opening than aftermath... "Noah" is associated with the Bible so people went to see it opening weekend. But, word of mouth as to it not being what many thought it would biblically be, more or less tanked it.
IMHO, I don't think it is a matter of Relativity not believing in the film; they most likely did. But, again, they went into it with eyes wide open as to the target audience and where it would play best for the best financial cost risk.
On a side note... many biker groups, who first saw MGP, became detractors of the film because it was not about bikers. That info. I got from two friends who associate with two different biker groups and received "through the grapevine" to skip it.
Erik's Ebony Eyes