First off, I can't be happier that the New England Patriots failed in their quest to become "the greatest team of all-time". For the record, I said all along that the Pats were not going to win the Super Bowl. But, I'm not here to gloat. There are some very basic answers to why the Patriots failed on the biggest stage in sports.
The Giants got to Tom Brady and made him work for everything they got. If you saw the games that NE almost lost, each team got to rattle Brady. He is not a fan of being hit and loses his cool when he gets popped in the mouth a few times.
How many times were they asked about perfection down the stretch of the season and the playoffs? Did you notice it has been a long time since they blew a team out like they did in September and October. Not only does that question get old, but then they start being a bit conservative which makes them prone to mistakes. The only reason they didn't lose in the regular season is that the Giants, Ravens, and Eagles made crucial mistakes at the end...far worse than the Pats. They were lucky to win those games. They didn't beat those teams, those teams beat themselves with stupid mistakes.
Pressure. They can say what they want, but they folded under the pressure of perfection. They played their worst game in two years against the Giants. If the elderly Pats defense can hold a team to 17 points, the Pats offense usually has that many by the middle of the second quarter. Their Super Bowl game plan was horrendous. They played not to lose and lost.
Lastly, they were the victims of karma. Call me crazy, but I just can't see a team that cheats like they did get rewarded at the end. Yes, they did cheat. $750,000 in fines means they did. What better way to get back at the Pats then to have them taste perfection only to rip it away from them when everyone is watching. You may not believe in the "higher power". Think about the 2007 Patriots. They were laughing their way to immortality until "something" drop kicked them off the ole karma train. Bill must believe, he couldn't even stay until the end!