oh, we as a market have every ability to change the status quo, but yelling at a developer to change, then buying their games which are counter-productive to our argument is never going to work. Expecting a minority market is going to impact the entire industry is just dreaming, you'll just become a niche. And calling for action without doing anything is lazy. People who work on games can make change, definetly, and we can encourage that change, but not by blaming them.
Speaking up is an action. Having a popular site like RPS speak up is an action. Having talks on the subject at the "Game Developer Conference" in an action, because that's where, you know, game developers go to talk about development of games, which is the issue here. And maybe they only got the courage to speak up at GDC because enough sites like RPS spoke up first, and maybe RPS only felt comfortable being this activist about the issue because they saw what is going on in foruns like these. Or maybe not, maybe it was just a collective realization that something is wrong.
Yelling at a developer after buying the game might send a message about their next game, that we liked their game, but it could be better if only this was different. And they might take that into account on making their next game, or don't. Maybe because their focus testing tells different, maybe because the publisher doesn't want to risk the investment, maybe because, as a person, they don't want to make a game thinking "what if the player is a girl?", maybe they don't actually know how to answer this question and despiste wanting to make that game, they have to ignore it and make another game about dudes.
And finally, if there is no product on the shelf that reflects what you want, you'll obviously "vote with your wallet" on one that comes close. On the thing that appeal to your taste in genre, story, gameplay, etc etc, but doesn't appeal to my taste in diversity. Maybe I'll pre-order this game anyway, maybe I would only pre-order if it had a girl on the cover, but now I'll wait for the 75% sale on steam, or maybe I got it for free while buying it as a pre-order reward for the game that do have the girl on the cover.
I can't put a note on my credit card number saying "look, I'm buying this game, but you'll better improve on the diversity issue next time or I will not buy it anymore". But I can buy it and them go to a forum and whine about it, but oh, we got back to the beggining, where this is no action, this is nothing, this blaming, etc etc. Except it is, there just isn't this concrete ratio of "whining:change" like there isn't this "buying:staying-the-same" ratio.
Stuff is complex and the fanbase speaking up is part of it. It is not all, but it is not nothing.