I guess it largely comes down to how you see the cause and effect working in that sequence of events.
You could say it was because everything about it was directed at boys so it made it something boys got into more than girls even though girls would be just as likely to naturally and instinctively get into gaming if it weren't pushed towards boys only. Or you could see that boys are naturally and instinctively more into the kind of stuff that defines video games (competition, battle, pattern recognition, playing the alpha, playing the hero, mathematical and analytical thinking, problem solving, etc) so boys were the ones who actually gravitated towards things like computers and programming and started creating and playing video games in the first place, and companies naturally aimed their product at their core market (the people instinctively creating and playing these first games), and what we see is that largely naturally playing out as it would even if it weren't directed as such.
I guess it's like we could say girls only like and play tea party games where they act like mummy and every one of the dolls is treated like a baby because we've brainwashed them into thinking they like tea party games and being like a mummy and then we sold them tea party sets and dolls. But I see it the other way around entirely: Girls like doing that stuff naturally (play mummy, feed and nurture, etc) so companies sell to their audience what their audience wants--for the most part.
So, the cause and effect.
I think ["proper"] video games (so not counting utter crap like Coin Endless Masher or Cardassians 2.0) are predominantly a boys thing by their very nature and always will be. But that doesn't mean some girls won't or can't enjoy video games too, or even that the percentages developing and playing games won't or can't change a bit either. I just think the 75-25% split that we're seeing above seems about right, especially when it comes to making video games (and certainly with the programming stuff), and indeed far more authentic than expecting or trying to aim [force] for anything more "equal" and closer to 50/50.
I only see thinking of 50/50 in this case as being somehow "better" as a bad thing because I don't think it's actually authentic at all--and a fake/forced/artificial/disingenuous world and society misguidedly pushing for 50/50 in every facet of human life, even just thinking of the gaming industry and community, is not even close to being better imo.