I was taught to carry one for emergencies. If your credit card gets frozen/lost/stolen/hits its limit, and you don't have enough cash for what you need, carrying a check seems like a good backup plan. Or it did until I've now learned it's essentially useless.
Take for example draining batteries until they die as the "battery health best practice". Obviously terrible advice for lithium-ion batteries.
Or advice to "never leave a car/lead-acid battery on concrete for longer than a few minutes." Which just doesn't apply with plastic/rubber shelled lead-acid batteries these days.
I'm not sure what a stop gap to replace the emergency check is, but I'm sure there are options.
That one vendor does not represent US society at large. Plenty of organizations (namely the US govt) still prefers checks. Gardeners, lawyers, and more...all take checks. I still keep a couple in my wallet for emergencies.