Why Christian films are traditionally bad:

Marketing.

Christians who pay to watch Christian films do so because they want a Hallmark-esque, feel-good experience. They want that feeling they get after leaving a powerful Sunday service, spiritually rejuvenated. Unfortunately, dialogue, plot, character development, and themes are always geared to the layman which often results in child-like storytelling. I don't think a lot of Christian filmmakers lack knowledge on film theory, I just think they just have no use for it. You can make a Christian film with subtle intellectual themes, unpredictable dialogue, and artsy cinematography but it probably won't make a lot of money.

Of the many reasons I stopped being a Christian, not being able to watch or make the films I want because of my Christianity is one of them. I can't think of anything more artistically constricting.