Because in a story you generally don’t want your characters to be as vapid as a puddle of water, like people who make one trait their entire personality.
Having a character with a varied personality makes it easier for people to view them as an actual person, rather than just a narrative tool, which makes them take the characters struggles more seriously.
Some people in real life make their sexuality their entire persona.
Those people exist.
Why shouldn’t they be allowed to be a protagonist?
Because in a story you generally don’t want your characters to be as vapid as a puddle of water, like people who make one trait their entire personality.
Having a character with a varied personality makes it easier for people to view them as an actual person, rather than just a narrative tool, which makes them take the characters struggles more seriously.
The other person said it better than I ever could.
But also: they can be a protagonist. It’s just that these movies are usually pretty shit.