Women are okay with sharing one desirable man (polygyny). It has been that way since humans exist, as evidenced by the different rate of reproductive success for men and women respectively, as recorded in our genome. This is stable from a biological and social standpoint, if the social environment is how we spent the last couple of hundreds of thousands of years: in clans and tribes, size below Dunbar's number. If you look closely, polygyny is making its comeback since the end of enforced monogamy.

For modern society, this return to acting out the ancestral environment makes everything unstable. I predict in my lifetime for depression and suicide to be overtaken in number by extreme bouts of violence and riots.

> wouldn't it be better for them to lower expectations?

There's two metrics here though which influence and confuse one another. Women get plenty of attention on the attractiveness side, but just because you can get laid doesn't mean you can get a relationship. It makes sense that if a lot of people are acting as suitors that you would then down select from this group. The problem is that on the woman's side you don't know if the suitor is looking for a relationship or just to get laid. Without a good metric for that, you can't properly down select and might just end up with a pool of only people that want to get laid. Especially if the primary initial selecting criteria is simply attractiveness (i.e. you're using an app). This is probably unsurprising considering in the digital world we often convince ourselves that we have stronger relationships because of tools like these (e.g. keeping up with friends more because Facebook) but in reality we don't because we are sacrificing the only meaningful tool to build and maintain relationships: physical time together.

Yes. But it takes time. Most importantly, women lose their ability to have children earlier than men but in their early 20s many of them are busy with other things and think they have a lot of time.

They get less desirable as time goes by so when they decide to ‘get serious’ at 35 it is already getting late

Tricky. In an environment where it takes time to collect information about competitiveness, updating of expectations is slow (and costly, because it is hard to be rational about this), there is a lot of randomness, and one's own competitiveness might be typically decreasing ... the slope of the expectation update might be not steep enough.

A common tendency is for women to become accustomed to the type of men she can find for casual sex online, it's rough to go from dating the top few to an average partner.

I'm sure they are aware of the situation as well as their own biological clock and are acting according to their desires. Unfortunately we have to just let people make their own decisions in the realm of dating. Maybe the future is common egg freezing or artificial wombs and people can delay serious families until their 40s or 50s.