Basically, it's going to be about the financial situation the Patriots now find themselves in — all by their own doing in recent years by poor draftings and throwing millions of dollars (AntonioBrown) against the wall offensively. That's also part of the reason why Brady decided to part ways with the Patriots without much of a fight. After seeing the Patriots get involved but ultimately sit on the sidelines again while the likes of DeAndreHopkins and StefonDiggs were easily acquired by other teams, and watching the Patriots spend their available cap space to franchise tag a guard in Joe Thuney, Brady knew nothing was really going to change from last season, when he was miserable without much help around him.
So Brady exited stage left seeking a better situation with a helping hand from Belichick. And now the head coach is without an experienced starter.