Why do 99% of movies follow the same formula?

Because they address our most basic anxieties, our fear of death and our drive to deny it.  Denial of death is what I call a meta-institution. That means an institution (defined by Veblen as a crystallized habit of thought or life) that is globally dominant and pervasive. No place, country, society, culture or whatever group is immune.  We all create and nurture death-denying institutions. Sometimes they involve religion, sometimes not. Business is as good at death denial as religion is. There is no way that the film industry can escape our basic drive to deny death.

Death doesn’t necessarily mean what happens to you when your brain and body stop functioning. It can mean poverty or social death and isolation. In this sense death denies us the good life but leaves us, zombie-like, to live out our physical lives with not much of anything interesting to experience or for which to look forward.

The film industry barters in death, social or physical, worldly or eternal. So, you’ll often see a person die in movies but generally that’s considered a sacrifice for the survival of our favourite death-denying meta-institution, the one that promises us eternal life of one kind or another. The hero, that person or group that personifies the triumph over death, occasionally dies in a movie, but always with the proviso that what they’ve fought and died for lives on. From war movies to romantic comedies, the formula is always the same as is the outcome. Of course there is a lot of variation in how the formula plays out and how long an individual movie spends on any particular part of the formula, but that doesn’t negate the existence of the formula itself.

Triumph over complacency, attack from various quarters (earthly or otherwise), disease, rejection, isolation, poverty, or what-have-you, is the bread and butter of the film industry.