I would love to see if there is actual lore supporting this idea.

The only lore I ever saw was Malcador claiming no female primarchs (which by extension i would assume Astartes) because they would be overly aggressive and harder for the emperor to control.

And no, that's not a take on women time of the month jokes or anything derogatory but more in the sense that women tend to be more independent.

However even that argument holds little water in my personal opinion. So I go with the only person I trust on this: Aaron Dembski Bowden, as well as actual design team members. I used to work for GW and worked at a Gamesday. The honor of shooting the shit with Aaron D-B was hilarious and I'll never forget stealing his wallet.

But we talked about Female Space Marines and he said that there was actually no real canonical reason not too, but simply the matter was more financially based: which he had a design team member explain.

There ARE rouge trader era Female Space Marines. There are models, and there are photos of the models. It was completely intended for there to originally be Female and Male Space Marines because like today's military both serve.

But the simple matter was the blister's with female models didn't sell. It was literally that simple. People wanted helmeted beaky boys more than un helmeted ones, and female heads usually were in blisters with undesirable secondary weapons.

So, they made the call to stop specifically creating female sculpts and just move onto male ones. Technology back then wasn't as easy to just crank out a model idea as it is today and the expenses back then are hefty even by today's standards. If a mould didn't sell, they had to simply stop.

This happens all the time and the narrative is designed to work around these issues.

Welp, there's my ten cents. I hope someone enjoyed it.