Swipe only is very rare in my neck of the woods (only one I can remember is someone at a craft fair in the past year who still only had the original square stripe reader). Perhaps you’re thinking of places that don’t support tap to pay but only chip (and thus don’t support Apple Pay)? Those I run into all the time (looking at you, Lowes and Home Depot).

Not sure of the last swipe-only reader I used, but it's still there as a fallback on many of them if chip and/or tap doesn't work for some reason.

Gas pumps were the last holdouts on swipe reads, in my area anyway.

My son was recently telling me he still knows of people who use the original Square swipe reader on their phone, which surprised me as I had guessed Square no longer supported it, and many phones don't even have the 3.5mm headphone jack that the reader plugs into.

Ha! I’ve used that phraseology for yeeears and only just learned about the Masonic connection. I think it’s safe to say that it has fully entered the common vernacular.

The microphone part of the jack provides a small amount of power to serve as a microphone bias. This can be used to power a few small analog electronics as needed. The mag stripe reader may not have needed anything but a reader coil, though, and the phone can probably decode the "sound" that comes from swiping the magnetic stripe.