Well of course I beg to differ! LOL. Some people, like me, will just never be fast miler's or 5K runners no matter the training. Someone asked me if I was doing the Jack Daniels Mile Race last night and I said, "it takes me 2 miles to warm up."
I don't run marathons "just to finish." I try to beat my time, every time, and qualify for Boston. I agree that the training is time consuming and can definitely see why some people don't run them and prefer shorter, but for me, halves and fulls are my distance of choice.
That being said, I don't get Ultras. I don't want to run for 12 or 24 hours straight and eat sandwiches and candy bars while I relax mid-race or take a nap in my tent and change my socks. And trail running just sounds like "hey, let's go get injured," to me. But to each his or her own. :)
Both distances are challenging. Training for and running a fast mile is intense with lots of speed intervals on tracks needed to pr. Marathon training can't be properly done without months of scheduled training and the absolutely essential long runs of 18 to 24 miles which pretty much wipes you out for that (usually weekend)day. I don't perform well in either discipline, my sweet spot is 10 k to half marathon. Lots of awe and respect to those who do well in those events....Is a sub 2 marathon humanly possible? Seems out of the realm of human possibilities but so did a sub 4 mile for over a hundred years!