It's kind of three fold for me.
First, like mentioned, it's the challenge. I look at it like extended range bow hunting.
Second, like also mentioned, it's the pleasure of having to work just a little bit harder to be successful.
Third, it's a bit of a protest. With all the hype of "long range" shooting, I vowed to put the hunt back into hunting and not just the shooting. Sure it takes skill with your gun to make an extended range shot, but really how much HUNTING skill does it take to get within 1,000yds. of ANY animal.