This is a bit of a chicken and egg, but the number of iOS users who have saved a web app or PWA to their home screen is probably in the single-digits worldwide. Half-joking.
People are just not aware that this is a thing, and when they learn it's a thing, they don't want to do it.
People are just not aware that this is a thing, and when they learn it's a thing, they don't want to do it.