Two Irregulars have asked the question that is the title of this post. (Well, actually, one asked "400 - Why?")
The following is my response:
I think the best (non)answer I can give to that question/wonderment is "turn it around on one's own self". Why are you doing the tough athletic things that you do? The answer you give yourself is very likely similar to the answer that another gives to themself as to why they do what they do.
But, I think that if you consider my case, you will agree that since I can't swim, that since my leg issues that sometimes bother on the bike are worse when I run, and that I am clearly more suited physically and mentally to marathon-like events than shorter events, the rando series becomes almost logical.
See you on the flip side,