Most consumer spending runs through Visa/MasterCard credit or debit cards; the interchange fee is baked into the prices of consumer products. Most people have something that processes as MC/Visa (whether it is backed by a traditional bank account, line of credit, or non-check-writing account) but most people cannot accept such payments, and no one can accept them for free.
Tech-savvy consumers can pay each other small amounts of money through Venmo and Square Cash, and that is typically how smartphone-native millennials settle restaurant bills and alcohol purchases among each other. They are free, but you can't move more than a few grand. Very large organizations usually have a web portal where you can type your checking account and routing number to pull money from your bank account with 3-5 day latency through ACH. Perversely, many of them will charge a "convenience fee" for this service that is not applied to payments by check. This is also strictly less secure than payment by check, because it's at least a little bit difficult to get authentic-looking checks for account numbers that are not mine. I can type whatever I want into the box on your website.
Most consumer bank accounts have an Online Bill Pay feature with the ability to push money to organizations of this kind of size. Sometimes they work by transferring your money to a service provider who physically prints and mails a check on your behalf. Usually they're just the Push (rather than Pull) variant of ACH.
Only some banks have the ability to push ACH transfers by account and routing number, letting you pay smaller-time recipients (as long as they trust you with their account number). Sometimes you can also input an email address, and the bank emails them asking for the account details to push the payment to (because that's not reminiscent of a phishing scam at all).
There are plenty of uses cases not served by any of these options. The car dealership. The family member you're supporting. Your small-time landlord, or the friend you're subletting from. Small town governments, suburban school districts, etc. I'd guess most adults don't use checks frequently, but we still need them every once in a while.
Pretty much only get cheques from charities/clubs now, haven't written one in maybe 10 years.