Because it's a great way to escape the crushing existential dread of a 9-to-5, only to face an existential dread of running out of breath.
Also, it's a great way to experience the thrill of slowly realizing you've been running in circles for the past 20 minutes, only to end up back at your start location.
And, let's be real, who doesn't love the feeling of their legs burning like they're on fire, only to be reminded that it's just a minor case of why-it-hurts?
So, go ahead, take it from the top, and try to outrun the impending doom of middle age. It might just work. Prophesize your success, or failure, and see what happens.
Or, you know, just stay home, eat a bagel, and pretend you're already an old person with creaky joints. That works too.