Because having one player tie up 20-25% of your team payroll means an awful lot of eggs in one basket. High risk.
Sure, I get that, but this is a move the Twins HAD to make. A home town kid, a superstar and the best catcher in the game right now and a HUGE draw in Minnesota. He's earned a contract like this. Injuries are part of the game, I'm not denying that, but they can't let him go, that's the bigger risk, IMO. The only position player I'd rather have on my team right now is Pujols.
The Mauer vs. Giambi/Pavano/Hampton comparisons don't quite mesh with me either. Mauer is one of the best players in the game, period. Giambi, Pavano and Hampton were all very good players, but never to the level Mauer is.