Confidence and security
This is a topic I've been putting some thought into lately. When out for local hikes/runs (like the guy in the original post), if I carry anything at all, it's a small knapsack with dog stuff, water, maybe some snacks and a map, perhaps more, depending on the expected weather and season. I don't carry many of the things that I would normally pack for a "real" hike. The "real" day hike pack contains items for first aid and safety. A few weeks ago, I wrenched an ankle about 3 miles into a local hike. As I returned to my car I was thinking that I'd've been all set if I were out for a real hike because that pack has Vetrap and hiking poles, which I don't bother to carry locally. I'd've taped it and used the poles to get out, instead of doing hours of dog-assisted hobbling. Luckily I was in a fairly busy area, I hope someone would have helped if I'd asked. Mostly, though, for local hikes I go to areas where I'm not likely to see people. Sometimes I bushwhack through the woods rather than staying along traveled areas, which makes being found even less likely. For a real hike, I leave an itinerary and schedule with someone, which isn't always practical for local outings.
Should I carry the day hike pack with its attendant safety gear for local outings - probably. Have I since - no. I'm not sure why, I would never head out for a real hike without it. And yet locally there's a smaller chance that I'd be found, or could find help. Perhaps a (mistaken) sense of confidence in the places I know well.
On the other hand, where do you draw the line? Should I carry safety gear on a 4 mile dog walk in the woods across the road from home? What about the walk to the mailbox?