A big part of it is nerve/brain response, in my own personal experience, though sure, a different walking technique makes a difference too.
I started wearing mostly thin soled shoes a few years ago: simple leather moccasins, $5 Chinese canvas shoes, Vibram Five Fingers. (I don’t typically walk around outside barefoot.)
When I first started, if I walked barefoot, stepping on a tiny pebble was painful. Wearing thin-soled shoes itself let me very dramatically feel the ground in a way I didn’t when wearing stiff-bottomoed shoes. Now, a few years later, the effect is much reduced, even though the skin on the bottom of my foot is not noticeably more callused than before. I can notice how the ground feels if I pay careful conscious attention to it, but it’s not constantly in my mind as I walk around.
I think the walking barefoot -> calluses idea is exaggerated in popular imagination. I have a friend who does significant amounts of barefoot trail running, and frequently run barefoot on pavement. His feet are also not obviously more callused than anyone else’s.
I can say that to get thick skin on your feet you need to not wear shoes at all for long periods of time and walk/run lots over harsh ground. I would go the entire summer without wearing shoes and running around all day and it would take a month to get thick skin on my feet and it would still be getting thicker by the end of summer. I would start wearing shoes and within a month my feet were back to a more standard thinness.
You do retain the careful walking/running skill, but without the thick skin you can't really run effectively on gravel, etc.
I started wearing mostly thin soled shoes a few years ago: simple leather moccasins, $5 Chinese canvas shoes, Vibram Five Fingers. (I don’t typically walk around outside barefoot.)
When I first started, if I walked barefoot, stepping on a tiny pebble was painful. Wearing thin-soled shoes itself let me very dramatically feel the ground in a way I didn’t when wearing stiff-bottomoed shoes. Now, a few years later, the effect is much reduced, even though the skin on the bottom of my foot is not noticeably more callused than before. I can notice how the ground feels if I pay careful conscious attention to it, but it’s not constantly in my mind as I walk around.
I think the walking barefoot -> calluses idea is exaggerated in popular imagination. I have a friend who does significant amounts of barefoot trail running, and frequently run barefoot on pavement. His feet are also not obviously more callused than anyone else’s.