First, there is the wonderful reality that he now lives close enough to do such a thing. But more than that, I realized how much I relish a custom that has vanished to the extent that even its replacement (calling someone on the phone without texting them first) is on the way out.
In the old days, dropping in was how you stayed in touch, the original face time. As someone on the shy/introverted end of the sociability scale, this sometimes gave me fits. I once lived in a mountaintop community where people not only dropped by but walked right into your house unannounced. While that was taking things a bit too far, I'd rather have that than no dropping in at all.
(One home I dropped in on a few years ago.)