I assume you're talking about movie franchises.

You might not want the same director for each movie. Maybe you want to switch up the tone or style. Maybe a sequel is really different than the original. Maybe the director wants too much money to come back, maybe the director wants to leave to other projects, maybe the director sucks and you want them gone

Is there benefit to consistency? Yes in some cases, sure, but there's also benefit in change.

Lastly, in fast movie franchises, there's realistic time considerations. These can take a really long time to make and many people simply don't want to devote 5-10 years of their life to a single project.

For the time consideration there's also the practical aspect of it. Movies like in the Marvel Cinematic Universe are being filmed at a really fast rate with overlapping filming and production timelines, and that requires additional staff - one person can't direct two or three movies simultaneously.

MCU is actually a bad example here. Because generally directors are tied to a single property there (like say Black Panther or Thor), which isn't on a breakneck timeline. MCU all exists in the same universe, but its not really a franchise in the same manner. Additionally MCU just kinda does stuff different than anyone else since its less of a director-focused/owned project.

For your suggestion, a thing like Star Wars 7-9 is more a valid thing as these are all sorta happening at the same time so they need to divide the work to get it on time.

Consider this, you have a director who makes your first movie. The first movie makes hundreds of millions of dollars at the box office, and is a huge success. Now, the director wants triple the salary to make the 2nd movie. Do you pay it? Or do you hire someone else at 1/3 the cost, and just tell him to try to make the tone consistent?

Also, directors are artists. Many artists don't want to spend 10 years making the same product over and over again. You do one movie, you get the experience, and then you move on to something new.

Say you do pay it. Then the next film doesn't do as a well. Now you're salty you paid so much for poor results, and don't hire that director back for the next film.

A great point! Yes!

The Star Trek: The Next Generation films had this problem. Jonathan Frakes, the actor who played William Riker for 7 seasons on the television series, was given the director's job for TNG movies #2 and #3 (movie #1 was a crossover with the original 1960s Star Trek). A director unrelated to Star Trek was given the nod for movie #4, but the film did poorly and effectively ended the TNG franchise.

It would have made sense to keep the same director-- someone who had been part of the franchise for 15 years and done 2 successful movies, right? But no, the producer wanted "fresh blood," and so picked the director who made Executive Decision, the movie with Stephen Segall on all the posters but who spent only the first 10 minutes in the film. (I'm still bitter.)

So an answer to your question is, "Because of producers who base their decision on their 'gut' or 'feelings'."

[deleted]