If you never asked this question someone else probably will, like your family or friends. Do you run because because it’s inexpensive? Because you don’t need to travel? To be part of a group? Feynman once said "Physics is like sex. Sure, it may give some practical results, but that’s not why we do it". Maybe the same could be said for running. Certainly it is not done strictly for practical reasons.
Is there something that sets running apart from other sports?
Maybe it's just a good combination elements. Eventually you'll be doing a little bit of everything. Sprinting, easy runs, tempo, fartleks, mountain runs, pancake-flat jogs. It's all there. You can spend as much time and money on it as you want. Some people drive 10 hours to race for 45 seconds and others run 25 miles from their front door. A race can happen over a 200 meter loop or a hundred miles.
Some runs are long, some are fast. Sometimes it's all about pushing through the pain while other days it's all about finesse. And running makes every other sport seem a little easier. Armstrong said the hardest thing he did was run the NYC marathon. That says something about running.