I pay cash at the filling station, at the grocery store, at restaurants, and more. Why? Because it tends to be faster. While others are waiting for their card to clear through the computer I've got my change and I'm gone.
On what planet do you live? How is going inside, waiting in line, paying for gas, pumping it, and going back inside and waiting again for your change faster than just swiping your card at the pump (or holding your phone up to the NFC reader), pumping your gas, and hanging the nozzle back up when you're done? For the others, you're trusting that the people involved can do basic arithmetic quickly enough and accurately enough to get your change right in a timely manner. On the occasions that I do pay cash, if I hand over $4.10 instead of $4.00 for a $3.85 purchase, maybe half the time I get a blank stare in return. Hand them plastic and you don't burden their feeble minds with having to make sense of that.
There are plenty of good reasons to hang onto cash, but transaction speed isn't one of them.