Well, I know that from my experiences dealing with cheaters on other servers from an administrative point of view, the excuse that I got from most people that did it was that they just wanted to expedite the process of getting materials for building. It is admittedly tedious to make a mine, go searching for an extended period of time, and not actually know if you're really going to find anything worthwhile throughout the entire search. You could find a cave laden with minerals, or you could get unlucky and not find a damn thing for an hour and a half. Both situations have happened to me.
I have always been a proponent of building over collecting. Minecraft to me, personally, is not about breaking stone rocks for hours on end to find some gold to make a few powered tracks, it's about building a massive, complex structure with powered tracks that you can label as a roller coaster and show off to other people. In the end, what I have seen is that people care a hell of a lot less about where the crap to make a building came from and a whole lot more about whether or not it's impressively large/complex and/or useful. People that do those kinds of things, I find, are usually just interested in skipping all of the really boring bits, such as spending hours at a time in a mine searching for diamonds and gold to sell to get the money for materials for building (because the mining of materials, without an x-ray pack, by far takes the longest time out of any step in the process), and they just want to get to the point where they can show off their building talents without having to worry about running out of funding.
This is the main reason I can see for supporting it's use, and I can definitely see the merits, although I also understand the drawbacks of being able to get ahead of other players quickly (a remedy for which would easily be just allowing all players to use them, as some servers do, although that is a bit of a tangent). It is often the will of the owners, in the end, that gets imprinted upon the server's policies, though, and it's nearly impossible to convince them otherwise to change their own personal convictions. It's how each server gets it's uniqueness, though, so it really comes down to a tradeoff of "am I going to give up a personal belief in order to give the players something else to use, or am I going to hold my own and keep the server how I personally like it?"
Each choice has it's merits and it's disadvantages. Who's to say what the right one is?
