Willie McGinest tells TMZ Sports he understands why Tom Brady and Rob Gronkowski left the Patriots for the Bucs ... saying straight-up New England is a GRIND!!!
"You work your ass off," the former Pats superstar says. "In that system, in that organization, you work hard. And, there's a lot of pressure put on you."
Don't get it twisted ... Willie says that's why the Patriots are so damn good -- they treat every player the same way and expect results all across the board.