Star Wars

Short Answer: A stand-alone Leia movie is missing from the Star Wars franchise.

If you go to the Disney+ streaming service's Star Wars section, you can see two options, the Skywalker Saga and the Darth Vader Saga. So those two characters' stories are told pretty much in full.

They made a Han Solo, um, solo movie. They are making a series about Obi-Wan. They made a series about Boba Fett, who clocked four lines and six minutes of screen time in his first feature apearance. And one about the Mandalorian who was not even part of the franchise until he got his own show. 

There are even cartoon series about the droids and Ewoks.

And then there is a character who has been (spoilers) a princess, a senator, a general, and a Jedi.

Who has neither a stand-alone movie nor a series. 

Since Leia's debut in the 1977 movie, we have had female action heroes lead Alien and Terminator franchises all the way up through, and past, Hunger Games. Wonder Woman, Black Widow, Captain Marvel... let's just say no one has a problem with women kicking some butt.

And yet, here we are. After all this time and all these movies, none focus on Leia.

Yes, Carrie Fisher is gone, but Harrison Ford did not play Young Han in the Solo movie. Clearly, the movie-- or series of movies-- would focus on Leia's rise to prominence in so many areas, from diplomacy to espionage to war. Are you telling me there would not be a war among actors vying to play Young Leia?

Go back and look at the poster from the 1977 movie. Almost every character there who is human has their own movie or show. Carrie Fisher gets one of the three top-billing slots. 

The title is already there: Leia: A Star Wars Story. There are numerous novels in which she is the protagonist, which could be used as the basis of a script. She's one of the most widely known characters there is, in any medium.

As has been pointed out by others... Princess Leia is now a Disney Princess. And those movies usually do pretty well.