It takes up the whole day. You've got to buy a decent pair of boots and a pack at the very least. Then you carry a bunch of weight up steep terrain for basically no reason. And no matter what, you always get a least a little sunburned.
So then what's the appeal? You're not proving anything to anybody by hauling some water bottles to a place that's been visited by so many people they decided to mark it as a trail. And there are better ways to get exercize that don't take up so much time and resources.
Of course, I should pause here to note that middle aged-old people have a set facination with the natural world. It starts around 40-50, when they begin watching the weather chanel as though it's a hit sitcom, and before you know it they're dragging all the children/grandchildren in sight to drive up into the mountains to "see the trees changing color." They're like Pokemon for the elderly.
For me, the important part of the hiking experience* is the sudden realization that this place, and in fact most of the natural world, really doesn't give a crap about me. It is full of things older and deeper than I will ever be, and whatever my problems, plans, or concerns, they are all laughably small.