I think over time (most likely after Mauer is retired in a few years) the real story will come out. And I do think its 3 things that have led to his decline:
1) Target Field. Fences are way too high and deep for him to have the power numbers he put up in his final years at the dome. He went from homeruns that were 5-10 feet over the wall in left, to warning track outs at Target Field. And there’s no close proximity “baggy” in Right to hit the ball off of for an easy double.
2) Zone defenses. Now that he doesn’t have the dome’s dimensions to keep the fielders honest, they can shift to all of his spots on the field where he hits the ball… i. e. up the middle, or to Left field, etc. Look how Alex Gordon owns him now.
3) Its not that he doesn’t care, it isn’t that he’s lazy with a fat contract. I’m almost certain there is an underlying health problem that we will all get more clarification some day from him, or most likely the team, after he retires. Concussion syndrome, bi-lateral leg issues … Neuropathy, an STD, who knows… but I DO think there is something more than we all already know. He didn’t like the label of being called a wimp that he got a couple years ago, so he just plays through it and doesn’t say anything.
All this being said, if I were Joe and hitting .275 and 10 HR’s a year – I would re-structure my contract for half the money (and only through incentives in hitting his old numbers, could he earn $23m again). This would allow the team more room to sign an additional front line pitcher, and provide a better chance to make it to a World Series during his career.
But again, that’s what I would do and probably not what any major leaguer would..