Diapers are called diapers because diaper means a type of cloth that was worn to catch pee and poop in the older diapers.
The word diaper originates to English from Greek diaspros (from dia 'across' + aspros 'white') to medieval Latin diasprum, to Old French diapre.
In the UK diapers are called nappies which is a napkin that was worn to keep the baby protected from peeing on their clothes or pooping on their clothes.
The word diaper was also the term for a pattern of repeated, rhombic shapes, and later came to describe white cotton or linen fabric with this pattern.
Cloth diapers were most commonly used before the invention of disposable diapers and the cloth diapers required a lot of work.
Then in 1948 Johnson & Johnson introduces first mass-marketed disposable diaper in the U.S.
Then in 1961 Procter & Gamble unveiled Pampers. In 1970: American babies go through 350,000 tons of disposable diapers, making up 0.3% of U.S. municipal waste.
Disposable diapers keep the baby much drier and prevent diaper rash and so disposable diapers while they cost money they are worth it.