I think that the reasons vary between countries.
China, India. Has an imbalance because girls are not wanted.
Why are girls not wanted? Because they are lower value.
So a societal shift needs to happen to change that.
I have also read that women are proritising getting an education and a good job. So that's a result of women getting more opportunities.
India, ditto.
In Japan, women are choosing not to marry as it curtails life. They are wanting freedom, to work etc. The male reaction to this has not been to change with this, instead many just shut themselves away.
www.google.com/amp/s/www.nytimes.com/2019/08/03/world/asia/japan-single-women-marriage.amp.html
In the UK and other similar countries, it's again a reaction to women's gains.
Women can earn their own money and have good lifestyles with lots of friends etc. They are choosier about who they date.
I see all of this as a reaction to women's gains in society. We are capable of looking after ourselves and when we meet men think, is life better with this bloke.
Remember that married men are happier than single men while the opposite is true of women.
Rather than upping their game, seems that lots of men feel angry and cheated. Entitlement.
Example. My friends experience of online dating has been awful. Dick pics, weird questions, lies etc etc
This idea that it's all about when looking for older men and the young ones are not in the picture is not something I see in my life at all. What I do see is women being more choosy because they don't 'need' a man. They earn their own money.
Also most women I know are married etc etc
The angry men definitely seem to have unrealistic expectations.
So I basically don't really agree with a lot of these comments.
I put it down to a backlash against women getting more opportunities. And rather than men upping their game, some seem to sulk, blame women, and want for women to be put back down again.