|"Sorry, but your father's in another castle."|
There was plenty of conflict between the protagonist and his bandmates, his fans, the priest at his church, and the choir kids. What, then, was the problem?
At issue was the fact that this guy started out being vain, selfish, and dislikable. He ended up as... well, vain, selfish, and dislikable. There are plenty of reasons behind why audiences go to see films: the visual effects, if it's based on an existing franchise with a built-in audience, a particular actor, and so on.
But I maintain that there's only one reason as to why audiences like a given story, whether high-budget studio or low-budget indie:
Over the course of your entire narrative (macrocosmic) and in every scene (microcosmic), your character must change. They cannot leave a scene, emotionally, the same way in which they entered it. They cannot leave your script, emotionally, the same way, either.
Look at Star Wars. In episodes IV through VI, Luke goes from country farmboy to savior of the galaxy and possessor of great wisdom. From angry and impulsive to cautious and measured. From hasty to responsible. Luke undergoes experiences, shakily walks the path of wisdom, then turns around and offers that wisdom to others. A nice, clean arc. Audiences like arcs.
In episodes I through III, however, we meet Luke's father, Anakin. Anakin starts out as angry, narcissistic, and whiny. In episode II, he's angry, narcissistic, whiny, and homicidal. In episode III, he's angry, narcissistic, whiny, and genocidal. Anakin doesn't arc. Sure, the new trilogy was a commercial blockbuster, but because of the built-in Star Wars brand. If episode I came out first and you had no further context, would the franchise have been taken seriously? How would you have convinced your friends to go see a film about a little boy and his six-foot, floppy-eared, frog friend trying to fight an army of droids?
To step back for a moment, consider that an audience, knowingly or not, projects itself onto your protagonist. A viewer can't help it. It's normal and natural. Whether a film, play, or novel, we instinctively search out bits of information about your protagonist that tell us, "I'm just like you. I want to be better than what I am."
By extension, I posit that it's far easier for your audience to like your protagonist, indeed to project themselves onto and invest themselves in the plight of your protagonist, if you make them relatable. How better to make a character relatable than to change them. And not only to change them, but to change their outlook on something to which we all relate.
The Harry Potter series is about a young man coming to terms with his own mortality. Will he master himself or fall prey to fear, as his nemesis has?
The Lord of the Rings series is about a young Hobbit coming to terms with desire. Will he master himself or fall prey to it, as his nemesis has?
Eternal Sunshine of the Spotless Mind is about a young man coming to terms with the inevitability of how relationships change. Will he accept it or give up, as his former girlfriend apparently has?
The Shawshank Redemption is about a falsely convicted felon attempting to maintain hope in a hopeless situation. Will he keep it alive or give up, as the warden and guards want him to do?
If your plot question is whether your protagonist will succeed in his/her physical journey, your thematic question is: will your protagonist grow?
If you want to write something commercially (and critically) successful, your characters must change. Simple as that.