I'm venturing a guess, based on his playstyle and chosen path of lifestyle... he's just a min/maxer who only looks for the next "stat upgrade" and that's it.
Pet Battles, fishing, cooking and Challenge modes don't offer gear-stat upgrades... and I'm betting that's all he wants. Those things offer this thing called "fun"... and there's no time for fun when you got to get to the top! :P
A motivational speaker I like describes this mentality perfectly: He spent his his whole time racing up to the top of the ladder only to discover that the ladder was placed against the wrong wall.
Just like his real-life... he does school and maxes his stats, then comes home and maxes his stats in WoW.
Can't waste time on things like enjoying cooking a home-cooked meal, or watching a sunset, or having a laugh with friends... those things apparently don't increase your GPA or DPS statistics.
(obviously they do help increase those stats... but you can't tell somebody like this that they don't because things like "morale" and "happiness" are not an identifiable measurable calculable statistic.)
But that's OK - it's these people who eventually keep the therapists and marriage councilors well-fed. ^_^