That’s because people in many countries don’t have access to clean water. There’s no reason to pressure women in developed countries to breastfeed for 2 years.
Unless you’d like to push them out of the workforce.
No, it's because there are a lot of scientific results correlating it to all kinds of better health outcomes both for the child and the mother, also in developed countries.
Whether this benefit is worth the great burden two years of breastfeeding imposes on women is, of course, debatable, and each woman should choose and not be questioned on their decision (as people often do). But sweeping the issue under the rug by denying the proven benefits of extended breastfeeding is not helpful.
Not when you adjust for education and SES and nothing beyond one year. Which is great news, because as you say, it can be burdensome.
(Not a knock on extended breastfeeding itself. I think mother and baby should breastfeed as long as it’s working for both of them - well into the toddler+ years if that’s what mom wants. But claiming unproven benefits is actively harmful to women.)
Unless you’d like to push them out of the workforce.