I want to qualify this.
I have a daughter, I've seen her friends. In my judgment, they are heterosexually motivated young females--there is not any obvious preference or aversion to young men--quite the contrary in many cases. By contrast, my brother's daughter, about 31, was recently married to another young woman, and the behavioral differences, while not marked or exaggerated, we evident.
So I'm limiting the discussion to heterosexually aligned young males and females.
I've once participated in a questionnaire of social appropriateness with my daughter, and was surprised as how negatively she viewed such normal practices from my day like a male in initiating a conversation on a long elevator passage, or in line at a coffee shop, etc.
Now, almost always the responses I got ranged from friendly to a bit reserved--which I took to mean that I should not extend the conversation. But to her and other of her peers, this was categorized on the survey as "creepy".
It's very difficult for me to get boxed in with people, like on an elevator or in a closed conveyance, and not at least initiate a conversation, which I'll quickly break off if I detect any alarm (this has never happened) or aloofness--which I take to be a female's tasteful way of limiting the exchange. For me to ignore others, male or female, artificially is disrespectful; they deserve at least acknowledgement for their existence.
Also, meeting males at bars or other social venues is thought to be abnormal. Introductions must come first (not a bad idea) and this is most often thru social media, not directly.
But the real core of the problem (if it is one) is that males, for whatever reason, are not taking the traditional initiative--they do not make reasonable approaches. Perhaps this is fear of being rebuffed (this is always a male fear, but eventually you get over it), or worse, they simply watch too much online porn. I hope this is not the case, but..
Anyway, this is what I think I'm seeing.
I see this in younger women also.