But at late 40's do these men feel like they have to choose between children and early retirement?
Furthermore, most men don't just wait around until their late 40's to find a young woman to reproduce with. Human relationships aren't this calculated. You don't get to plan when you end up meeting the right person. Life happens. There are plenty of men in their 30's in committed relationships with women in their 30's. Just because he can delay reproducing doesn't mean they can. Usually this is a decision that a couple makes together. And I haven't heard a man say that he had to choose between his career and having kids because his wife's biological clock was ticking.
Or, to put it more simply: why don't men leave their careers to have children at any age?
Most men don't leave their careers at any age because they have to provide for the preganant wife which can't work and needs lots of care.
But even assuming the whole business of giving birth took a whole year (the full nine months for carrying a baby to term and another three to recover) there is no reason that this has to be the end of a woman's career for good. It's one year. People take one year sabbaticals and go and gawp at Machu Picchu. It's not the end of the world, especially if you're young and even in a fast-moving career like STEM academia. it's not like you can't ever read the latest publications again because you have to lie in bed for a few days after giving birth.
The care you say men must give to their wives lasts at best a few months of a year. After that a man is free to leave work to raise the kids and the woman can go back to work, if they so wish.
So why don't they do it?
Then there's 8 weeks of recuperation after birth, paid by the health insurance which are more or less mandatory and it would be stupid not to take them. Even if the body's not fully recovered at this point, the woman can work.
The question is, why would a mother leave her newborn in order to work, when the outcome will be worse both for the mother (weaker bonding, working through recuperation) and the baby (missing its mother during the day)? That's why it's common here that women either take one or two full years of parental leave or they stay at home N years. This can also be and is mixed with part-time work.
In any case, that would be an easy pregnancy. Childbirth over 30 becomes harder and over 35 it's classified as a high-risk pregnancy.
"After that a man is free to leave work to raise the kids and the woman can go back to work, if they so wish. So why don't they do it?"
One reason could be that by the time those months (in reality a year) are over the mother's better at caring for the child than the father.
I've also seen that women tend to like spending time with their babies(!) so they prefer working part-time or staying at home.
Finally, it's often the case that the husband earns more. Women also tend to prefer men which are successful. In the case where she earns more, it makes economical sense for the husband to work part-time or stay at home. I read an article about such a case a while ago, and being a stay at home dad looked like a sad existence: besides the social disdain and emasculation, that person wasn't even welcome to spend time with other parents (i.e. mothers), because they were looked on with suspicion.
I agree with your sentiment, but there's a big biological difference here in terms of the fertility age. As discussed in the article, this question is very urgent for women in their 30s, but men can delay reproduction until their late 40s with no major issues. As such, men don't face an ultimatum on this, the way that women do.