I don't understand why so many people think "pdf" automatically means "A4" or "letter size" document. PDF's are size agnostic. Storage is cheap and so is proces

I don't understand why so many people think "pdf" automatically means "A4" or "letter size" document. PDF's are size agnostic. Storage is cheap and so is processing power. A phone-sized pdf will be 20 mb instead of 1 mb, but so what? It's a small price to pay for quality typesetting. Similarly, pdf's can be sized for the now typical 16:9 laptop screen.