The circumstances are entirely different.
1) Tuna was leaving to compete in the NFL, in fact in the same division. Fairbanks was simply returning to college, and would not compete against the Patriots.
2) According to Wikipedia John Hannah contends Sullivan "took Chuck's authority away and turned him into a liar." by forcing him to renege on the contract. Kraft/Parcells was a good old fashioned power struggle, but Kraft never took away power away that was Parcell's.
3) Parcells was playing the media and intentionally forcing a disruption to the team, while Fairbanks would have been delighted to amicably break up, keep it internally and not hurt the season.
You can't blame Fairbanks from wanting to get rid of that idiocy from his life. The college hiring season plus the perceived right job became available. Yeah Fairbanks was naive to trust the Sullivans, but he built a football powerhouse from ashes, drafting and coaching. None of what happened was his fault, and it basically ruined his life because he was probably on his way to a Super Bowl, and after was forever a failure.
Don't blame the victim!