100 mpw is not easy. There may be a few times in your life when everything is going well, and it feels easy for a while. But overall it isn't. Do you really think that the reason most people, even fairly serious runners, run significantly less than 100 mpw, is because they just haven't figured out how easy it is?
I'll disagree with some of the others on this thread and state that 100 mpw, even if you do only "easy" miles and no workouts, is still not easy. Why? Because it's tiring! I feel like that is the elephant in the room that everybody is ignoring, or refusing to admit. It is TIRING to run 100 mpw on top of living your life. Yeah, you may have few months where everything is going great, and you get the impression that running isn't tiring, but in the long run, 100 easy miles a week is a tiring routine for the majority of people, and on top of that, it starts to feel like you are constantly either running or getting prepared for a run, which gets kind of tiresome.