The disadvantages of Christian movies is there are limitations on topics and subject matter that secular movies don't have. Secular movies have full allowance of creativity in every avenue. Christian movie makers have to follow much stricter guidelines, some because it may cross a biblical border, but also many to pacify other Christians.
And while it is possible to make quality movies within this smaller spectrum, it takes top writers, actors and directors to make it work. Something Christian movies typically don't have. And even within the secular community, and all that they have available, it's rare to see that done well.
For a Christian movies to push the boundaries, even in a way to show the bad guy as a bad guy, often risks pushing it too far. For instance in the 90's a movie came out staring Carman, a Christian wannabe Rocky movie. While his opponent was this loud, ego-centric womanizer. So to establish this they showed him with scantily clad women sitting around him. And they showed him filming a 'commercial' for an in movie product called 'Whoop
@ss'. This required the character to say the product name over and over and over, while holding the can with the name printed on it. As well as showing him getting drunk. Many Christians were offended for they had taken their children to see the movie, not expecting these things.
Not only did it backfire and upset many Christians, it came off as cheesy and didn't really set him up to be the bad guy they were trying to get across. He came across more as a professional wrestlers character, than a professional boxer and genuinely bad person.
So those are the kinds of things out of their control.
The thing i think also turns many off is nearly every Christian movie i've ever seen interjects a scene about preaching and it changes into more of a break from the movie, than a scene in the movie. And done so in a way that is more about tickling emotions more than anything more sincere.
For example i recently put a movie on on Netflix. Some random movie i came across. Riots breaking out and roving bands of people going house to house murdering people. One man has prepared his family for such types of events and they manage to escape into the woods. It all seemed a good movie, then i began noticing small things they were saying and doing. Eventually i realized it was a Christian movie. It was edgy subject matter, showed some violence related to the story and put the subjects in a situation that seemed genuinely tense. I was surprised it was Christian. It was too good. And i figured out it was Christian because they kept slipping in small things. You realize they are a Christian family, but due to the events, one of them begins to question God. And it shows these disagreements and discussions that seemed natural to the film. But near the end they started stacking up on the preachy-ness. And, in true Christian movie fashion, they took a break from the movie to make a drawn out 'spiritual' scene and get preachy. And on top of that it was done in such a cheesy manner, making it more awkward. If they'd stuck to those smaller interactions it would've been good and still gotten a message across.
And that's what makes them so bad. It's a niche target group, which makes it unable to become better. Because the rules that restrict it and force it to conform to that niche group.
Think about B movies. Those are targeted towards fans of B movies, not the average big budget movie goer. It's a niche group and thus can't grow.
Even in the 80s with Christian rock and metal, so much of it was so cheesy with it's lyrical delivery. Same thing with Christian movies.