The demographics for the Sims 4 comes as no surprise.
Sims 1/2/3 had more supernatural/fantasy gameplay, silly hi-jinks, and comical consequences, so the demographic was a bit more varied (including a more mature age group). Whereas the Sims 4 has been watered down to accommodate a more family/kid friendly play style. That's the choice EA made with this particular iteration and we either accept it or move on. And generally speaking, females/feminine types tend to be drawn towards that type of gameplay (family, nurture, dressup, romance, etc), so of course that's who the largest demographic ends up to be.
Companies will market their games/products to the largest audience and cater to the loudest squeaky wheels. All others (outliers) will get a few crumbs tossed their way once in a while to keep them playing/buying the product too (albeit they're not the main revenue). But it's like this in every industry, not just the Sims and not just gaming.... figure out who your largest demographic is (or choose who you want as your target audience) and aim the majority of your products and marketing strategies in that direction to draw even more of that demographic in.
I guess I'm a bit of an outlier as a Sims 4 player because even though I'm a female, I'm not much of a family player. For a few hours here and there? Sure, but not constantly all the time. I'm more drawn towards fantastical adventures and comical pandemonium. So the supernatural, and silly hijinx aspects of the Sims 1/2/3/4 is what has kept me around for so many years... even though there's less of it in the Sims 4, I'm still enjoying the bits that we do have.
As a side note:
Because of the more family/kid friendly direction of the Sims 4, I'm betting the next iteration of the game (Sims 5) will be even more geared towards that same demographic and will have hardly any (if at all) supernatural/occult/hi-jinks type of gameplay. We're already seeing that partially play out in the Sims 4 with such a lack of occult/supernatural DLC's, the reduction of humourous consequences.... and more importantly, the nerfing out of these things when they have been added because of the larger, louder audience demands on social media to get rid of them.
I think the 'us vs them' problem that has plagued the Sims 4 since the beginning is going to get resolved in the Sims 5 by simply omitting one side altogether. :|
Just my $.02 worth.
