This has been a question I've asked myself since reaching my goal weight of 140, and now under 140, for the last 3-4 months. I haven't lost all the fat yet, still 1-2 lbs left to lose which will take most of the rest of this year at the rate I lose it now.
The first is about reaching 60 where time and age catches up with the body and it's a slow decline from now on. It's really simple, every morning I get get better or get worse. It's not really that simple because after 60 you're only slowing the decline of time and age of your body and mind.
The second is I've driven the weight and fat below my genetic predisposition, so after not walking for a few days, the body will begin to readjust to add both back. I feel it at the 3-4 day mark where it takes a few walking days to get the body back.
So walking is keeping the weight and fat off, and hopefully losing the remaining fat over the spring and summer. Walks are now for sustaining what I've gained. The third is a followup to the second, the less weight, the less pressure on the lower back and Sciatic nerve.
The last is simply it's good mental and physical exercise. I'm basically lazy, and can be a good couch potato, so forcing myself to get up and ready and then get out the door to walk 6-8 miles helps remind me who's in control.
Anyway, that's the thoughts on the walk this morning when a couple asked me why I walk so much. It makes my day.