It's because our grandparents (perhaps even our parents) were raised in the era of "waste not - want not". You just never knew when that luxury item would be your last. In an era of soup lines and respectable hard working people losing their life savings - tomorrow was uncertain.
My folks saved the foil wrappers from gum and string from packaging. Every kitchen had a ball of both. They were not only saving for their own use, they were saving to help others. Aluminum foil was donated to the war effort. I have no idea what the millions of balls of string were used for - perhaps it made a great baseball in lean times.
Much of that era's need to save "for a rainy day” was subconsciously passed on to my generation. We, too, had that embedded fear that tomorrow was not certain and the economy might falter making luxury items impossible to buy.
While that might be true, I had an awakening many years ago when I read an Erma Bombeck article about how she wished she had used those things and enjoyed them before they got all icky from years of waiting for the right moment. I believe Ms. Bombeck was in ill health when she pinned this.
And although I had a college professor make fun of my using Erma Bombeck as quote worthy, she certainly knew human nature.
“Waste not - want not” is simply using what is available at the time. The unused perfume becomes too strong to ever use. The never used china doesn’t give your own children/grandchildren a lasting memory. Killing violets deprives us of one of the most beautiful fragrant flowers. Saving the hunk of expensive cheese gives you a hunk of mold. And it goes on. Saving precious consumables doesn't save for bad times, it wastes. It wastes the money someone spent on the item, it wastes the potential enjoyment, and it wastes a memory.
What it does not do is help you store up for an emergency. By the time an emergency comes, consumables are past consuming. And that's the difference. Save the foil gum wrappers for recycling if you want, but chew that gum before it becomes so hard it will break your tooth. Erma Bombeck was right.