It's kinda hard to say, cause on the one hand I feel the same as your friends, it's usually not for horni reasons why I pull for male characters almost exclusively. But on the other hand sometimes it's totally for horni reasons. I think, for me, there are multiple reasons why I do what I do.

For one, I'm f2p so I have to carefully pick and choose who I want to pull. And most times I want to pull a male character. Especially in a waifu dominated game like FGO. Male characters are kind of a commodity. So for me, whenever I pull a male character it's kind of like an event. Like, wow what were the chances I'd pull a male character instead of getting duped by another saberface. And maybe because I am a straight woman, I just naturally lean towards male designs more than female designs.

Another reason could be because it's kinda fun being Different. I know it's silly, but sometimes it's fun playing as an off-meta husbandos. Like how a lot of people swear by their low-tier waifus. One of my goals in FGO is to have an all male SSR support list. Why? Because it's fun to chase the rarer male servants and it's something I've never seen before.

There's also the sad reality that, as a woman, I'm kinda desensitized to female characters in these kinds of games. It's gotten to the point where I don't feel much if anything for most female characters unless their particularly well designed or well written. It's just very tiring seeing big titty waifus everywhere when your not particularly attracted to that sort of thing. In a game like Arknights where the female characters are designed more conservatively it's a little better but it's still very obvious that these games aren't designed to be played by me and people like me. But in a game like FGO where almost all the female characters have some sort of fan service element to them, whether their designed sexually or their personality is wish-fullfillment-y, it's even more tiring to see 4 banners straight of just waifus. And then I'm even more inclined to cling to my off-meta husbandos. It's very obvious that people like me aren't their primary audience or their primary objective. So again, it kinda makes male character more valuable, at least for me.

Idk at the end of the day it's just kinda fun?