It's a video game, not a historical reenactment. They can include women. It's not like there's not other elements that are ridiculously unrealistic.
If you wanted to be realistic they could include women disguised as men, since that did happen. But realism and video games isn't really something that goes together.
You might as well just say any WWII games can't have black characters unless they are in a unit with only other black characters. But don't you think that would be racist? Why hold different standards for female representation.
Also, while Elder Scrolls Online is terrible, the rest of the games are awesome, go get them, you will enjoy them.
A few points in response:
1. Depicting historical racism is not racist. Whitewashing it and pretending it didn't happen is racist (avoiding Godwin's law here, but think of certain people's views of what happened - or should I say did not happen - during WW2 and how offensive that is to the victims' families). The past was horrible. The same is true for women - showing the horrible sexism of the past tells us how bad it was. Some US army units were racially integrated from the battle of the bulge onwards anyway, so who does not know history?
2. No, no, no, big numbers of women did NOT dress as men to fight. There is ZERO evidence that this was common. I once heard of a woman reaching the trenches in WW1 disguised as a man, but that was 1 out of millions and I cannot verify that account. Medical examinations would have caught most women who tried, and few tried in the first place. The only British woman to fight in WW1 as a soldier was Flora Sandes, who fought openly as a woman in Serbia. The Serbian and Russian armies openly used women soldiers in combat, hence why I specified the Western Front.
3. I saw friends playing elder scrolls and it looked very centred on slaughter, but the slaughter was very unengaging; there was no real skill to combat, just bashing cluelessly at the enemy's armour or throwing spells at him until he died. No grappling, no half-swording and stabbing through gaps in the armour, no proper defence and riposte. Bashing somebody's arm had the same effect as bashing his foot. Most of the weapons and armour looked stupid as well.