I think we all know that most vacuums today are never as well built as the old ones. Even today, things like microwave ovens, shavers, mobile phones, hand mixers and even toasters aren't as well built as they used to be - but we didn't have as cheap manufacture as we do now.
Even when Hoover brought out their plastic hard box uprights they made claims that they were lighter to push/lift because of the manufacture and trying to steer the buyers away from "the last of the classic uprights."
But then when you look back, homes in general didn't have half of the expensive premium floor coverings available now, either, or for that matter laminate flooring - vinyl or lino existed a lot as it is cheap covering (and still is) but it isn't going to suit everyone nowadays.
Then there's the air quality and what contributes to dust in the home.
I think today's vacuum cleaner has a lot more to pick up than what the 1970's homes had.