Either you vastly exaggerate the time savings of card payments, or credit card machines in your community are more reliable than what we have here. Don't brag too hard about living in the future, however, because here we often have the option of self-checkout, which typically is faster than even looking at a cashier. (Unless one of the oldsters who annoy you so has wandered into that lane and now contemplates the scanner as if it were the cockpit of the Space Shuttle. In that case one might offer assistance? Most of our self checkouts take cash!)
The day will come when all purchases will require the approval of several more parties than the buyer and the seller. We will not enjoy that circumstance, so people wiser (and perhaps less hurried?) than you will use cash as long as we can.
No need to create more CO2 for the packaging and transport of groceries to your door if the supermarket is on your way from work anyway. Plus you get to pick the exact fruits and veggies you like yourself.
I assume you have a US viewpoint where grocery delivery is common but this is not a thing for consumers in Austria outside of the capital. It also costs extra so there's that.