(Late-edge Boomer here): My parents and grandparents taught us all of these things growing up. But without the mean, shaming voice.
So as a result, we learned that we had a lot of choice and could save a lot of money. And we carried that practical knowledge into adulthood. By needing less money, we reduce the amount of leverage that a boss etc has over us.
The more economically/financially independent we are; the less dependent we are on centralized conveniences and electric appliances — the less anyone can force us to stick with toxic jobs, living situations, relationships, or other not-healthy gigs.
Also, there is a direct connection between fossil-fuel dependency (and dependency on consumption in general) and supporting war; propping up fascist regimes.
Plus, line-dried laundry just smells good. And, a weird but true fact I’ve noticed in my various side gigs cleaning houses over the years, having a washer + dryer just seems to induce some people to have more clothes and do laundry more often. I know it doesn’t make sense but I’ve seen it repeatedly.
The tone and manner in which something is delivered makes all the difference. And for what it’s worth, if you hear Boomers still saying this, then a lot of them are going against this advice — because a lot of my fellow Boomers are now totally dependent on AC and all that other stuff mentioned in the post.
PS. One thing I discovered almost 20 years ago is that since I don’t use air conditioning, I don’t need hot showers in the summer. And that led to not needing hot showers in the winter (since I live in a climate of mild winters).