A simplistic explanation is that previous high fertility rates were based on subjugation of the female populations. As that has relaxed women have decided not to have as many, or even any, children.

Why would men want to have more children than women?

Why don't you ask a woman about that?

They'd want to have sex, and contraception was unavailable or too expensive.

Women don't want to have sex?

Women don't necessarily want to have children... You don't have to plant seed in the field every time you plow it.

Also women's choice and reasoning behind mates tends to be different from the male section algorithm.

Often less, and it's more "expensive" to them in a no-contraceptives world because men don't get pregnant, and they (historically?) also had an unfavorable "workload/child" burden compared to the husband in general.

It's relatively recent that women are able to make that decision, or to reliably make the decision of whether sex is related to reproduction.

I don't know why, but quite a lot of men I know and even more that I read about seem to be obsessed with wanting kids more than any stereotypical chick brimming with estrogens would. They would totally divorce their wives if they hadn't given them children. I don't know how many of them dream of becoming a patriarch like them biblical people or something, but this is what it is /shrug

And that reduces male sperm count and quality how?

Can you explain the logic behind that question, because I can't see any.

What my original comment said was that we have a global fertility crisis, not due to social changes (although these also play a role), but because biologically a lot of people simply can not have children any more (or it's a lot more difficult than it used to be).

Responding that women's emancipation is the cause for very real global health issues was the non-sequitur here.

Your claim that total fertility rate being sub replacement rate mostly due to biological inability to have children is not seen in any data I have seen.

All the trends correspond directly to women’s emancipation (although men also probably want fewer children).

I am well aware that this is not a mainstream view (yet), but the rate of decline in fertility in the past 20 years is not something that can be explained through social changes alone. Even in Afghanistan fertility has taken a nosedive and the social situation for women there has definitely not improved.