They existed before debit cards and mostly before credit cards became popular.
Anyone paying with a check voluntarily these days is just either extremely stubborn and stuck in their ways, or incredibly ignorant. There isn't a single reason I know to keep doing it.
Avoiding processing fees for using a credit or debit card is another reason, although those are becoming far less common.
Currently I only use my checkbook to look up my routing and account number for some online subscriptions so I don't have to remember to update the payment method when cards expire.