With a sport or activity like cycling, you get to see so much of the world you may otherwise not see nor appreciate. And when I say see I mean you really get to SEE it. You can take the time to look around you and really take it all in. Yes, you can do the same with running, but the chances are, you’re not going to run 100km, and rarely are you going to see thing beyond 10km from your start point.
When you’re driving, your main concern is keeping your eyes on the road—ofcourse you’re doing that whilst cycling too, but you’re not travelling at nearly the same speed. And when driving, you don't often drive into the mountains just to see and appreciate the views, and if you do, you are stuck inside your car, with the noise and the knowledge that you are causing pollution. Whether that is something you’re concerned about is another topic.
Cycling is one of the only modes of transport I can think of whereby you can travel huge distances without it being an annoyance and which offers multiple benefits. One being fitness of course, and the others being the fact that it’s free—that trip is free, minus the cost of fuel/food—it’s not causing any damage to the environment and you can get fresh air and appreciate your surroundings.
The distances you travel on a bike are not annoying, like they would be in a car, because a car is a means to get some A-B in order to do something. A bike is to get from A-A by the most appropriate route required. By this I mean that you start at home and finish at home. Your goal, for example, might be to train climbing (going up hills/mountains), so you ride to some hills/mountains, ride up and down them, maybe stop for a coffee, or scones, and then ride home.
Runners get some of the same benefits, but they just don’t get to see as much. I can ride 50km in one direction and come across a vastly different scene than I might in the other direction.