First, who said that? Got link?
Second, why would you lock a male NPC to a specific demographic?
While I get the logic (character can end up more focused as a result), the fandom of this game that likes guys consists of both women, men and nonbinary folk. And those types of players already constitute for small percentage of playing populace. You are spreading yourself to thin for it to be worth it.
Lets look at Garret for example. A lot of men find him attractive and would like his content (a hardcore dom) yet he is only made for women which leads to him not being talked as much.
So you should try to pander to both with any of your male NPC. By which I mean is that you should make it so that anyone interested in them should get something out of it. Because if you do not, it leads to the feeling of dissonence between you and the game. This second thing will be harder to understand
Lets look at Elyon for example. While I like him, I always felt disjointed from him because I felt I was not the target audience. For when I play as a guy, he never touches my dick or makes any kind of remark on masculinity. I felt like the game was treating me as a girl.
Other examples include Takahiro and Quin.
Speaking of Quinn for second time in 2 days, I will also chalk his lack popularity to him being a strict pitcher. While yes, he is supposed to be somewhat dominant twink, denying us access to his bunny hole really hampers mine, and others, enjoyment of him. For while I do enjoy bottoming, him not doing same for us does feel exclusionary to guys and girls that enjoying topping/pegging. Which i do think hampers him in a long run. Since even people here feel disappointed at that fact.
As
Biostar said.
"Having a femme looking bunny boy downstairs and not having the option to ravage his boipussy is a whole other level of gay."
Like even Brint has bottoming content (and fantastic one at that) and he is this games definition of a "perfect stud". What is Quins excuse?
So yes, while at the end of the day male NPCs are never going to be as popular as female ones, I do feel like you could garner some sort of clout in this community by writing good male content that most people can enjoy. Or at least create some loyal fans towards your creations, ala Berwyn and Brint.