Also, I think if one is really intersted in a game, one does his/her research before going for the buy, no? So strictly speaking having a female in any of the vids should not really be necessary, as you'd be able to read it up and then enjoy your experience as whatever you prefer.
No, not really. It's not our obligation as female consumers to dig and poke through vaguely worded game press for scraps of representation buried under mountains of generic scruffy dudes. The onus of selling me a game, of convincing me that I should part with my money for your product, is on the producers and marketers of such games. There are games a'plenty in the market, if you want me to buy yours, show me why I should bother.
What a game that does not advertise its female protagonists is telling me is that it doesn't really care for my business. If they'll bother putting the time and resources into showing the male hero on video to convince guys to buy it, then bother showing me the female hero too. Convince me too. Telling me I should do my research because there's totally maybe possibly some chick buried under there too is just telling me that that poor female hero is an afterthought, as am I, and it's whatever whether I buy the game or not - as long as the male audience is not freaked out by womenz in their trailers, women can just go read a wiki or something.
So what happens then is that I simply don't buy such a game. Maybe I'm missing out on a cool game where I could have played as female, but if I'm whatever to a company, then that company is whatever to me too. Ultimately I'm not missing out on much by skipping a game or two, but that company sure is missing out on all the money I could be giving them. In the sum of gains and losses, for the minimal cost of showing me a female hero in a trailer, they've lost my business for their game, DLCs, microtransactions, sountracks, artbooks, t-shirts etc, and probably the rest of their game library too. They may not realize yet it because they haven't seen how much money I (we) have sunk into games that openly wecolme me (us) as a female gamer, but games that think throwing me a bone as a customer is not worth the effort are losing much more in the long run than I am.
This doesn't go just for female characters, either. People of color need to see themselves as poster heroes in game marketing too, not just be told that there's some skintone slider somewhere where you can look slightly orange. Queer people need to know upfront and clear that there's a new game out there where they can see their own lives on screen, not just be told that there may or may not be some obscure gay content hidden under layers of "safe" marketing. We all deserve the same respect and honesty every other player gets.
Don't let yourself be told to do your research. Don't take for yourself the responsibility of searching for reasons to buy a game, make the publishers and developers and marketers of such games hussle and sweat to convince you to buy their product. Make them show you loud and clear that they've got all these things you're interested in, instead of sweeping them under the rug and hoping you'll care enough to dig it out on your own.