Getting a little philosophical here, but staying to the point:
I believe that there is limited musical real estate. If a machine offers a longer loop (with the aim of providing variation) then it is taking up valueable real estate that could be used by the player, to "breathe" in his/her personality. The more a machine offers, the lesser space there is for the player to offer, following the law of "limited musical real estate", that i just dreamt up.
Expounding upon the previous statement, just because a machine offers more, it doesn't take away from/or add to the players talent, after all the player has more to manage, and thus, has to make more effort(relatively management vise) to produce a good quality piece.
Because I am a little claustrophobic, I, personally, require tremendous amounts of real estate so I can "breathe". Busy loops, or loops that try to be realistic (in emulating the "monster" as Uncle Dave put it) take up real estate. In that way can not a loop be realistic too, if it instead chooses to emulate the "beat keeper"?

Benz