I guess I'm just not seeing it as anything special because I'm already aware of the bias, and there are so many ways to manipulate such a loose definition.
I think if you ask a given person if there is gender bias in media, they'll say yeah. But the magnitude of it doesn't seem apparent to people, especially many guys I've noticed.
For example, someone will be like "Star Wars had strong women! Leia was strong, right?" But if I point out that just about every single person they encountered in every context was a dude in that trilogy, that there were three named women in 8 hours of film, it quantifies the issue a bit.
As has already been granted, some movies just inherently aren't going to score well int his area. Saving Private Ryan and The Shawshank Redemption, for example. No sane person would fault those movies as gender biased, because in context it makes sense. And if there's a movie with almost no characters in it, like the Disappearance of Alice Creed or something, then clearly nobody is going to fault that.
But when a significant percentage of long, complex movies have little or no female/female dialog, it shows a rather enormous bias in films and other fiction.
Males have wrote the bulk majority of fiction, especially prior to contemporary times, and it will have a male bias. I even know a high school director that will cast two girls for the same part because in most plays there are several male parts but at most a few female parts.
I don't consider that a reasonable excuse for them. I write stories and they don't have a female bias.
My longest story has a male protagonist and a male antagonist, but major parts from a variety of male and female characters. The wisest character is an old man. The most active antagonist (probably the character with the second largest share of the story besides the male protagonist and the most depth out of anyone) is a woman.
Another one has a male and female as equal protagonists.
Looking back at these stories, there was no effort to add males or females or make it gender balanced. At roughly 50% of the population each, in most contexts it would just naturally work out roughly that way if people weren't thinking from a gender-centric position. There is considerable male/male, female/male, and female/female interaction in all of my stories just by default, and I'd have to go out of my way to make a story so slanted towards one gender unless there was a very specific context (like a historical retelling of WW2 front combat lines) or a shorter story with a small number of characters.
And as for the works prior to contemporary times, they can get a bit of a pass but entirely new stories are coming out in the '80s, '90's, 00's, and 10's that still have the same weird ratio of men and women in movies.