@anon
Just to clarify, we're both talking about the comment section here on FSTDT, right? Because I don't really see anyone disgusted or refusing to know about female anatomy, just confused how not knowing an exact number makes them children. Its not like they don't know periods exist, and they have a general idea how it works, but of course they wouldn't know precise details. The responses to her original post are more or less a slew of incel-esque trolls who got offended and are purposely being obtuse, and is more a problem with assholes being assholes than the attitudes of men in general. Fair to call them childish? Yes. Fair to generalize that all men are like this based on their reaction? No.
I won't deny that there is an attitude that reinforces a separation of the sexes, which is a result of fundies being against sex education in general and praying for the return of outdated gender roles, but using the comments here as proof of that is really looking in the wrong place. As for your examples, learning about a significant other's culture really comes down to the individual. Knowing a generalization is similar to just knowing periods exist and a rough idea of how it works. Some people might be really into their culture and tell you the exact details of their menstrual cycle, and of course you'd oblige them, but most would be kind of freaked out if you came in one day wearing their traditional garb, speaking only in their native language, and telling them the average amount of time they keep a single tampon in them before changing it out.
I mean, I'm really sorry that you've never had a guy that offered to pick up some tampons for you, but it isn't fair to immediately assume its because he thinks periods are gross or because sexism. I dated a girl that was on several medications for various issues. I didn't keep tabs on her medicine because she did it herself and would ask me to pick up stuff if she so needed it. That didn't mean I didn't care about her needs, it was more she just handled it herself. Most guys are going to assume that you're just going to look after your supply of tampons or pads and let them know if you need any when they go to the store. If you get particularly bad ones, he's not going to know what to do about them unless you take the initiative to teach him. After a while of being with him, he'll get used to your routine and come back from the store with the exact kind of tampon you use, some Midol, and a tub of ice cream. If he refuses to anything like that, find a new boyfriend.