Keep in mind you're only talking about America among developed countries. All others have much more leave, maternity, sick days mandated by law, and people take them.
I think this notion is more widespread in other cultures (as you say, from many other more developed countries) and from that stems legislation. Based on my experiences, I do firmly believe that most of us would benefit by getting out of our home countries, more often and for longer.
“Vacations are for the affluent/rich”
Absolutely. But tens of millions of Americans are living paycheck to paycheck, so they can't even afford to take a week or two off and stay at home reading/relaxing/playing with the kids/whatever.
Basically, they are slaves, they just don't know it.
It is only the result of these choices that they 1) need paychecks and 2) have already spent those paychecks.
I have a friend that works on a fish boat for 4 months out of the year, and spends the rest of the year hiking.
I have a friend that teaches middle school, and spends the summer months travelling.
They probably make less money per year than the paycheck-to-paycheck person you have in mind, yet they have the time to travel because of their lack of obligations.
It sounds like you think someone that chooses to have a couple of kids and a stable household deserves to be in perpetual servitude.
Open your eyes. It's not like that elsewhere.
Don't worry! You'll be in the same situation someday, and then you will realize how ridiculous your statement is.