After twenty years of backpacking I quit in 2010. In the 90's I'd go hiking or backpacking in the Sierra once a month. In the early 00's I had a kid and carried him on my back as soon as he was old enough and he went on his first backpacking trip at 2 1/2. We kept up the monthly hiking trips and occasionally went backpacking in the summer. In 2008 we went backpacking three times.
I was never in very good shape, never kept up any kind of exercise regimen, and there's no consensus about proper nutrition. During or after every hike or day of backpacking I'd usually get sick with a headache, nausea and exhaustion. In the last few years I'd end up at camp violently vomiting, unable to sleep on the hard ground, hot and cold at the same time, forced to get up and pee every hour, and in the morning I'd get up exhausted, barely able to stumble back to the trailhead.
And emotionally I could never handle backpacking alone nor could I ever find anyone who liked it as much as I did. I gave up trying to invite others along when after two of my trips I never heard from the people I'd gone with again. Not because we argued or anything but simply because backpacking is hard and they hated it. They didn't get sick or have headaches, they just hated hiking, were "tired" which apparently means sleepy to some people, and were scared of the woods.
Homesickness, loneliness, shame, depression, and crippling social retardation are the only reasons I'm not heading out for the Pacific Crest Trail start next week. The only reason I didn't do it last year, the year before, or ten years ago. I have all the time, the money, the knowledge, the gumption to do it, but I can't even imagine wasting all that effort to plan for a five month backpacking trip, get down there and in a couple days hike out and fly home, because I miss my computer or wife or whatever.
In 2009 I started mountain biking and enjoy that a lot. I ride twice a week, almost always alone, though my wife and son have appropriate mountain bikes, but they've simply stopped going with me. The last time we went together was in January maybe.