I like to think there's 2 types of story/porn consumers (this applies to non-pornographic things too). People that like to place themselves in the shoes of the protagonist and immerse themselves, and people who like to follow the protagonist (or selection of characters) around to see what happens to them. Basically; first person consumers and third person consumers.
Needless to say that female protagonist games, or games that lack a protagonist, are pretty hard to enjoy for guys that belong in the first group. On the flip side, following a dude around all game can be less interesting for straight dudes in the second group. It's not really about downsides and upsides, mostly just preferences revolving around how people like to consume their porn or stories.
Also you can easily just have a game with a male protag and just one heroine with all the screentime to acheive your 'pro' of a female protag game. Which isn't that uncommon.