I shamble off down the street every day in a t-shirt and an old pair of trousers, with a dog on the end of a lead. We stop sometimes - he smells things, I look at cloud formations, the scenery, listen to the bird song... and we pass people who are "exercising."
I think it must be an American thing? For their health... most don't look too happy either. They have a strange, slightly stiff-legged walk like robots, look at their watches a lot, and wear very tight-fitting, brightly coloured clothing and $200+ trainers. They like earbuds or headphones to block out unwanted sounds too, like nature or that rapidly approaching truck/bus they haven't noticed.
Some of them jog. The only time you will see me jog is if there is someone chasing me with an axe.
I think if it's not fun, don't do it... how about you?