One reason I and a number of people do that: to cover the possibility you might be at the wrong door/house or ringing the wrong doorbell.
I had both of those problems at my previous residence. It was an apartment complex with some N½ addresses. Visitors would often miss that bit and be at the wrong door. On top of that, the doorbells were counterintuitive: they were arranged vertically, but the bottom doorbell would ring the top apartment and vice versa, so I forever had visitors and deliveries ringing the wrong bell (and actually mostly for the other units ringing mine.)
Also if someones just dropping by (unscheduled delivery, sales) and I'm asleep, or watching a movie, or whatever I don't want to be disturbed, and if I have a question for my neighbors similarly I don't want to bother them if they're busy. Phones have snooze mode, most doorbells I've encountered don't.
I usually text/call when I visit people not so often like once a year or once in couple years because usually I don’t remember exactly which number it was.
If I go somewhere couple times a year I usually feel quite comfortable using doorbell.
I had both of those problems at my previous residence. It was an apartment complex with some N½ addresses. Visitors would often miss that bit and be at the wrong door. On top of that, the doorbells were counterintuitive: they were arranged vertically, but the bottom doorbell would ring the top apartment and vice versa, so I forever had visitors and deliveries ringing the wrong bell (and actually mostly for the other units ringing mine.)