Question

How come all the staters are mainly male?

Comments

Because staters are better than starters.

Answer 1

Because there is a 87.5% of finding a male starter and just a 12.5% chance of getting a female one, so you will most likely be getting a male starter, however getting a female one isn't impossible.

Comments

+1 for percentages
I like numbers ^_^
As long as they're below 10 digits.

Answer 2

It's not a matter of how feminine or masculine they look; starter Pokemon are supposed to be rather exclusive and rare, so if they have a predominantly male population then they're more difficult to breed.

If you have a female starter, you can breed it with a lot of different Pokemon.
If you have a male starter, your only options are to find a female version of it, or get a Ditto.

The same goes for Eevee and fossil Pokemon, it's just to make them more difficult to obtain.

Answer 3

There is no official reason. You'd have to ask Game Freak for the real answer; so this is just another question falls under the "that's how Game Freak wanted it" radar.

Just notice how all the starters are not necessarily girly Pokemon, and most of them share traits that make them appear to be male rather than female.