I imagine that people have a number of different takes on this, but I'll toss mine out.
Even back in the N64 days, Matt seemed to have gotten really deep access to Nintendo. When the GameCube/Dolphin started up, Matt knew everything about it, and he started talking an awful lot about how the GameCube was going to be the greatest thing since sliced bread. He was practically oozing with optimism.
Also, and I'm not sure if this matters, but Matt became something of a god to a growing group of fanboys. If something was printed on IGN, it became an undeniable fact.
Then once the GameCube started not living up to his expectations, he started getting moody. You could feel it. The kicker was when he started an editorial series called
The Nintendo Difference, where he took Nintendo's slogan of the time, twisted it into an insult, and started ranting about everything that was wrong with Nintendo, which some of us already knew about and accepted, but Matt decided that all the kiddies really needed to know about.
To quote Matt "I concede that my views are jaded -- I've been covering Nintendo long enough to get this way. I really don't think a person can call himself or herself a true Nintendo fan without being so."
After that, he pretty much started talking on an infrequent basis about how the GameCube would've destroyed the PS2 had he been in charge of Nintendo. Every time people started complaing that he was crossing the line between "news" and "bitter editorial", he started putting himself up as a martyr, saying that he was the only one willing to speak the truth, and that the Nintendo kiddies are just too immature to accept it.
When he took over the IGN-Cube mailbag, things got much worse. Sometimes he doesn't even use any letters as an excuse to go on rants. People have complained about it, but he pretty much openly states that he has free reign over how to handle the mailbag, and intends to use it as his loosely-Nintendo-related blog.
He's taken shots at the DS in the GCN mailbag, predicting doom for the DS and Nintendo, without even owning a DS. He's spoken about how he thinks the Revolution is going down the wrong path, even while admitting that he doesn't actually know anything about the Revolution, or what path it's taking (Nintendo apparently locked him out this generation, along with everyone else).
Basically, he used to be a tremendous insider. Then he became a bitter, jaded, know-it-all.
Of course, I've heard people say I was an idiot for not realizing these things about Matt sooner.
I've been watching Matt go downhill since... 2002, apparently. And every time I start to feel that maybe I was reading to much into it, and I should just ignore him, he usually does or says something to up the ante.
It became a joke, saying that he was just starting a fuss to attract attention, and increase traffic to IGN, but it's gotten to the point where I seriously would not doubt if that was a motivation behind Matt's occasional controversy.
(BTW, the rest of IGN is a mixed bag of jerks and losers, with some good people probably mixed in, but nobody stands out as much as Matt.)