Okay I know this post is possibly dead ever since two years now but I actually can give a logical answer about this. Plus, it's my first comment so let's prosperity happen.
I've originally been seeking about starters' gender thingies, mainly because I plan to get a female Snivy in my future game of Pokemon White or Black (hasn't chosen yet) and I already got 2 females out of all the 5 starters I ever owned so far, so I believe to be luckying against the odds. (cuz yeah, 2/5 is about three or four times more than 1/8)
If you wonder though, I just "use" genders for aesthetic and my little imaginative world of mine. uvu (I don't focus on completing the 'Dex before I do everything else to be honest.)
Point is, I've made researches (that's how I'm a rather well-documented newbie (my first pkmn game began when 2019 begun)) and there is a simple explanation for both why did Game Freak do this and why would it be happening in-world.
I mean, of course Victini above (or below, idk) already answered about the reason GF did so: Unless one is a Ditto, only the female parent gives their species to the bred child. But what wasn't been said is that Ditto is itself a tad-bit-little harder to get than an "usual" Pokemon that'd be on the same group egg of whichever starter you would wanted to breed. In fact, it doesn't exist in Ruby/Sapphire (but does in Emerald) and is (apparently) only catchable-in-the-wild-but-not-after-a-whole-adventure in the Gen II games (and their remakes).
Too long didn't read version: You have one eighth of a chance of having that starter that wouldn't make you wait to beat the game/a side-quest/a trade (yes, "beat a trade") to make more of 'em. They're your journey pal, afterall, they got to live your journey before you try to make them kids.
Now for the in-universe explanation: It's basically the same.
If their rates would be 50/50, they would be easier to reproduce and wouldn't be so rare, as they are always described to be.
But I do admit that despite it being quite logic, it can be annoying when you want a girl but get a boy.
PS: Eevee is actually a 87m-12f ratio.