There's been a lot of debate on whether Marc Gasol should have won Defensive Player Of the Year, with the NBA's best and most popular player having a very strong candidacy. LeBron was deserving of the award and you would have heard no complaints from me had he won, but I think Marc Gasol was very deserving as well. I think the nature of defense makes deciding this award hard. On offense we generally regard someone as better by scoring more and doing it more efficiently, while on defense there's more variables at play. Honestly, I believe that some people didn't think Gasol should win by what I like to call the "ESPN dumbing down effect" which in short, is an emphasis on viewer driven content such as highlight plays, star players, etc. More highlights, more exposure, and more popularity does not necessarily mean better. No matter where you live in the United States, you could have watched LeBron play at least 30 times (on either NBATV, ESPN, TNT, ABC). A reason he's a favorite for DPOY is simply because more people have seen him play more often. On the other hand, if you have managed to watch Marc Gasol and the Grizzlies play 5 times then you are considered an expert on the matter. First I'll give you my opinion on why LeBron didn't win.
LeBron had a great defensive season, but it is wise to remember that in the past 15 years Metta World Peace (The artist formerly known as Ron Artest) has been the only perimeter player to win the award. No disrespect to LeBron but he didn't play defense at the same level of intensity as Ron Artest did for 48 minutes a game, 82 games a year. He had stretches where he did, but not as consistently or as often as Artest. It's relevant that Scottie Pippen also never won the award. DPOY seems to go to big men on defensive minded teams. Maybe it's not fair but neither is the fact that MVP's (NFL &NBA) go to offensive players or the fact that the Heisman, which is supposed to be given to the best college football player, is generally given to the quarterback who puts up the most video game-ish numbers regardless of scheme or other variables. The Miami Heat led the NBA in points per possession, effective field goal percentage (accounts for the fact that 3's are more valuable than 2's), and true shooting percentage (factors in free throws as well). In short, they are an offensive juggernaut. Most voters historically haven't felt comfortable giving DPOY to a player on the best offensive team in the league. This leads to my rationale on why Marc Gasol did deserve the award.
Honestly plenty of people think Marc Gasol shouldn't have won the award, because he's not a very popular player, neither is his team. Some say that he's not the best defensive player on his team, that it's Tony Allen. Tony Allen is automatically eliminated by the fact that he plays 26.7 minutes per game. No player has ever won a major award playing so little. I think that we get so caught up on highlights we forget the other things involved with defense. There's more to defense than highlight reel chase down blocks, playing the passing lane perfectly for a steal and getting a nice dunk on the other end. Every NBA team averages between 92 and 100 possessions per game, and some fans want to crown players great defenders because they make 2 or 3 steals/blocks, while forgetting there is still over 90 more plays. Playing great defense involves proper rotations, defending the paint area, properly showing on the pick & roll and then timing your recovery back to your man, and rebounding. Marc Gasol does all those things very well. Watching him guard the pick & roll (most effective and used play in basketball) is a masterpiece. His team gives up an NBA low 89.3 points a game. The Grizzlies were 6.8 points better defensively (per 100 possessions) when Marc Gasol was in the game. On a team that already does not give up many points that is remarkable. So while he may not necessarily be the best defender (is MVP always given to the best player?), Gasol is more valuable to his team's defense than LeBron (might have something to do with Battier, Chalmers, Wade, also being elite defenders).
Great defense unlike its offensive counterpart requires 5 players all playing well and together, it really is a team concept. Simply put, Marc Gasol was the best defensive player on the best defensive team. That is more than enough reason to why he is deserving of being DPOY.