Because MVP's a fluff award that's given, not earned, and the voters are biased against players who are too dominant. The fact that Shaq only got one MVP award and Jordan wasn't the recipient of every MVP award from 87-88 to 97-98 (excluding his two retirement seasons in the middle) blows the award's credibility to bits. Hell, after Jordan's 2nd retirement Shaq should have won the award every year from 98-99 to 02-03. He was clearly the most dominant, feared player in the NBA during that time. Instead, Duncan won two, he was damn good but Shaq was better, and an aging Karl Malone, who didn't even have a remarkable season by his standards, and Iverson's 42% FG percentage won it the other two times.
It's about novelty. For the sentimental, soft-headed tits that are in charge of handing out the award, having the same player win the award for X amount of years in a row would be dull. So the voters mix it up for the sake of novelty, with f*** all regard to objectivity or reason.
LeBron should be working on his fifth straight MVP right now. But the voters were assmad that LeBron told Cleveland to eat s***, so they handed it to Rose in 2011. Smart money's on Durant winning it this year, just because. It's ********.