So, someone on the Internet recently asked a forum of hockey fans that question. The post basically said "I'm a brand new hockey fan, I love hockey, everyone always boos your commissioner when he brings out the damn Stanley Cup, what gives?" Next thing I knew, I went into some sort of fugue, and when it was over, I had written an answer. Having written a wordy thing about hockey on the Internet, I figured I should come here and post it. So, here's what I said:
As I see it, there are more or less four key reasons people dislike the Commissioner:
1. Lockouts. The NHL was formed in 1917, and operated every single season until Gary Bettman took over as commissioner in 1993. Then there was a half-season lockout in 1994 and a full-season lockout in 2004-'05. The Stanley Cup has been awarded every single year since damn 1893 except for two: 1919, in which the Finals ended early due to a Spanish Flu epidemic; and 2005, because the NHL and NHLPA couldn't negotiate an agreement to play hockey. Lockouts may not be entirely be a commissioner's fault, but presiding over that kind of lack of hockey certainly doesn't help hockey fans like you.
2. Over-expansion. When Bettman took over, the league was at 24 teams. Since then, it expanded to Florida and Anaheim in 1993, moved three northern teams south from '95-'97, and expanded to Nashville, Atlanta, Columbus, and Minnesota over '98-2000, for a total of 30 teams. Many of these expansion franchises have done very poorly, most recently with Atlanta having to move back to Winnipeg (one of the northern cities a team left back in '95-'97). This has two really negative effects: a) it dilutes the talent pool, so it's going to add worse teams while making better teams worse, which is bad for the sport; b) it disenfranchises a ton of fans; you have abandoned fan-bases all over the place.
The thing with relocation of bad teams is that it's actually a good business idea. If there are always floundering teams at the bottom of the league, there are always businessmen looking to sell their teams, which means there's always a huge relocation fee for the NHL to collect. Look at the case of the Thrashers, who are being moved to an arena that seats only 15,015 because they weren't selling enough tickets at an average of 14,685. On the $110 million sale, the NHL makes a $60 million relocation fee. This is sustainable: teams lose a few million dollars a year, and after a decade or so, they are relocated to a city that was abandoned a decade prior, and the NHL makes a ton of money. Then, when they remain unsustainable, they are moved again, and the NHL keeps on profiting.
3. "The new NHL." You're right that Bettman has improved parity, but that's only good to a point. The natural conclusion of "adding parity," of course, is that every game is exactly as likely to end one way as another. That's not good for hockey, as at the end of the day you still want a team that is better at hockey to be more likely to win a hockey game. Adding randomness is not a good way to increase parity. Take the shootout for example: it's a new addition to hockey, and it's been statistically shown to be a random one. Most hockey fans that have been watching since before the most recent lockout, and almost all coaches and players, think the shootout is a ridiculous gimmick and there's nothing wrong with a game ending in a tie.
This extends to more than just the shootouts, though - penalty calling has also become more and more erratic over Bettman's tenure. We've seen little ticky-tack hooks and grabs get called every time in the name of making the game faster, which it has done, but it also means we have to see penalties called for dumb stuff like that. Meanwhile, as we've added a second referee on the ice for every game, we've seen a dilution of officiating talent, which combined with the increased speed of the game means that officials are just getting it wrong more often. This, again, has helped add to the parity of the sport, but is not good for the sport.
4. Personality. At the end of the day, there's a pretty general sentiment that Bettman just doesn't "get hockey." He was an NBA guy primarily, and he came to the NHL in the name of growing it as a business (which, as we've seen above, he's got a good sense for). He came here to grow an American market, but he doesn't understand how. Sometimes, as in the shootout, he tries to do so at the detriment of the game itself. Sometimes, on the other hand, he'll totally miss the mark on what Americans want, like when he tells a Bruin that he can't wear a Red Sox cap in an interview, or he signs a 10-year contract with Versus instead of letting hockey be shown on ESPN, which is where everyone in America watches sports.
The issue of personality is that we hockey fans feel like hockey's different from every other major sport, and we're fiercely proud of that, and at the end of the day, we feel like Bettman doesn't get it. This is shown in the way the league handles supplemental discipline, which seems more based on the offender's status in the media or the resulting injury than it does on the actual dirtiness of a given play. It's also shown in the way he's marketed the sport: we consider hockey to be the "ultimate team sport." The NHL is too often marketed just like the NBA: individual accomplishments, "Crosby vs. Ovechkin" and all that - the shootout, too, is all about one guy vs. one guy, which is why it's such an insulting end to a 65-minute match of the "ultimate team sport." Bettman's smug, condescending personality in every single public appearance doesn't help this any - it kinda communicates, "yeah, I run your sport; what are you gonna do about it?"
In other news, someone won the Stanley Cup Wednesday! I fucking love when someone wins the Stanley Cup! Woo!