Jealousy is surely a part of it, but a lot of people genuinely do not like the way BB carries himself. Everyone always makes a big deal about BB's "handshake" at the end of games, but let's face it: this is a sport that a ton of kids watch, and the Patriots are one of the most high-profile teams out there. It may just be appearances, but there are times when BB doesn't exhibit what could be called "excellent sportsmanship."
This is right off of the media "talking points" but is missing the real issue. Nobody would care about any of that stuff if they weren't told to care by the media. The media hates Belichick because he doesn't give the media what they want. And for the media members who cross him? They become dead to him.
How would you feel if you are Tom Jackson and you are not welcome in the locker room of potentially the greatest team ever? You would stew in your own bitterness until it became impossible to contain your distain for all things Patriot. After a Pats win, it is almost uncomfortable to watch him on set. Lately he is even getting angry at the teams that fail to beat the Pats, which is pretty comical.
The NFL (a media outlet in their own right) hates Belichick on a couple of fronts:
1) He doesn't support the NFL vision of information access. Assistant coaches, injury reports, etc.
2) He goes out of his way to present an image (bland press conferences, drab dress, impersonal on-field conduct, etc) that is counter to what the NFL wants.
3) He implicitly (and sometimes even explicitly) rails against rules implemented by the NFL. The punishment for Violationofoperatingproceduresgate was severe (and it was severe...saying the punishment was "light" was another media talking point) in order to stop his rebellion once and for all.
4) He is a vital part of the Patriots success and everyone knows it.
The NFL wants to market the excellence of their players and have coaches that help them do this. Until the explosion of the offense this year, the Pats were generally recognized for their preparation, gameplans and execution...meaning they won with less physical talent due to superior coaching and a high football IQ. Try marketing the NFL Network with that!
That is why the NFL loves the Colts so much. Big names doing big things on the field...with a lovable coach on the sidelines not getting in the way too much. "Get the punt team out there. Why are you waving at me? You don't want to punt? Um...OK. I guess we can go for it."
Like most things, it all comes down to money. Belichick is a barrier for the media and the NFL (as a media/marketing entity) maximizing their revenue. He doesn't care and they hate him for that. Since they control what the casual fan sees and hears, they put out the talking points (cheating, sportmanship, cold, calculating, evil, unappealing) and "everyone" hates Belichick. That is the price he pays for excellence. We should commend him for that.