We were pretty much lower middle class (sometimes lower-lower) , had friends who were better off and friends who were much worse off, and nobody really talked about money openly.

In my family I always figured it was WASP reticence, but now that you mention it I think it was something broader. Maybe: people with money don't need to talk about it, people without money are embarrassed to talk about it, and if you're somewhere in the middle you don't want to reveal your hand.

My father poured molten metal in a foundry as a married 19 year old.

That's entirely the point. Lawns originated in the middle ages as a status symbol. They demonstrated a) that you could afford to waste a perfectly useful piece of arable land and b) you could afford to pay a team of men to neatly scythe and shear it. It's hard to tell how much land an aristocrat actually owns, but the size of their lawn acted as a reasonable proxy.

The invention of the mechanical lawnmower helped to democratize the lawn, establishing it as a symbol of middle-class suburbia. A small lawn in front of a suburban house didn't demonstrate that you were gratuitously wealthy, but did demonstrate that a) you could afford a larger plot of land than strictly necessary to accommodate your house and b) you had leisure time to spare.