In a Japan seemingly obsessed with sex, few seem to indulge

Shame is prevalent in these cultures. It seems that many only want marriage and family on their own terms. Simply put they seem to be worried about making themselves poor, low-status, uncomfortable, and generally "losing face."

Humans worry about low/poor status because if you have a high status, you are a more desirable mate, and will have more and better procreation options.

You pass these on to your children, probably genetically, but certainly in a hereditary fashion (by teaching them to be status observant).

This works in small groups (not necessarily Dunbar's number, I suspect it scales past that).

But when you're no longer the hunter gatherer in a tribe of 150 people, or no longer the German peasant in a town of 1200 people... things change. When there are millions and billions of you, there still are only a few high status spots, still only a few more second tier spots. Thus, there's little chance of you gaining any of these, and a neurosis of sorts sets in. You postpone families until you can maybe gain higher status. And not everyone has to be like this for it to be bad, some smaller fraction of the whole might act like this... it has the effect of drying up the pool of available mates for other people who aren't going to wait for something better. They're dragged along, playing the same game, to some degree or another.

"Status" has changed too, even getting a chance at it now requires absurd resources. Think about how much a quant earns in NYC in a year, and calculate how many children you could comfortably raise in a South American country (even to the point of putting them through college and medical school). So chasing status, whether or not you get it, eats through whatever resources you might have that would have allowed children. All of this is self-reinforcing, of course, ending up with the next generation pursuing it to ever more extreme levels.

Those who don't chase status become much less desirable as mates.

A successful Japanese man maybe finally achieves the status he needs to have a family, and has no time to invest in raising one. Despite the relative wealth, maybe feels as if he can't afford it (or as large of one). If he does anyway, he can only start that later in life (after success), thus restricting how much time he has to attempt it (it will be smaller for this, on average).

Monkeys don't scale well.

As an extremely tentative first stab at "solving" what we on this board agree is a problem,

There is no solution.

To solve this, you'd have to become something other than human. This might even be a speciation event, I can't tell yet (if not that, then an extinction event).

It's strange to me that this isn't a more prevalent topic of conversation and this subreddit, for example, doesn't have 100,000+ members.

They celebrate it, if they're even aware of the phenomenon. Most aren't.

What the heck is going on here? (Pardon my French; I lose control sometimes.)

Japan, and specifically, overcrowded Tokyo could be a human real-life equivalent of the Behavioral Sink experiment by John Calhoun (see also more info here ). See some discussion about possible manifestations of this phenomenon in the human society here .