I think it came down to “happy wife, happy life”
As a lifelong Patriots fan, I'm ecstatic. Not because I didn't want him having success without the Patriots (I'm not vindictive, he did what was best for him), but now because I don't need to deal with any idiotic questions like "so you're rooting for the Bucs right? Brady fan over the Pats?"
Because no. I'm not a Brady fan over the Pats.
But good time to go out. He proved he could win without Belichick, and now his oldest son is about to start high school. One hell of a career, and he's been set for life money wise for ages.