> Most of the dud movies are broken at the script and actor selection phase.
Nothing kills a movie quite like a bad script. You can pair up a lot of very similar winners and losers and see that the key difference is the script. Compare for example Baywatch and 22 Jump Street. Both rehashed Gen-X era TV shows about good-looking people. 22 Jump Street was smart, self-aware, and successful.
Since few bombs do have good scripts, you would think studio execs would simply never put a weak script into production. While you can have a successful film with a shitty script, why risk it? Especially given how cheap it is to change a script early on.
Given that they seemingly don't, there's probably some other forces in play. Probably some combination of:
1. Maybe it's just really hard to evaluate a script early on. There's probably some truth to this, but I don't think much. Film execs read a lot of scripts and it's an easily trainable skill.
2. Maybe the script starts out good but gets screwed up because of perverse incentives. This is, I think, a bigger part of it. The director wants to put their mark on it. A big-name star wants their character to get more screen time. All of a sudden, there are forces pushing on the script that make it better for the people making the movie, but not for the view.
3. Corporate politics at the studio comes into play. A studio brings on a script doctor who is compelled to earn their check by making a certain amount of changes even if the script didn't need them. An exec owes someone a favor and gets a role jammed in for a particular actor. An exec got burned on a previous film about shark and says all sharks must be removed from all scripts.
4. Then the reality of production, scheduling and budget. You read a lot of stories about subplots that had to be cut because they ran out of money, scenes that were rushed because of location access, etc. I think a lot of times, the movie you watch is not the movie that was described on paper. It's not uncommon for screenwriters to take their name off a film because the final result of production hell isn't what they wrote.