I think having a checkbook used to be a basic part of being a functional adult, but there's a whole new generation of people that have never sent a check before.

There are still a lot of businesses and government agencies that require payments to be sent by check.

It's paying for convenience. Name any "basic adulting" task and I'll show you a service that can do it for you. House cleaning, taxes, groceries, laundry, childcare, etc.