Cooks had 2300 yards and 17 TD's with a 67% catch rate in his last 2 years in New Orleans.Stats don't tell the entire story. Look at Brees' stats for this year. They wouldn't tell you how bad he's struggled in his last 6 games.
Go back and watch that Detroit game. The only reason he had so many targets is because he threw a fit in the media the week before, complaining about not getting enough passes thrown to him. So they game planned to get him involved vs the Lions and it limited the offense.
That's a pretty compelling story.
Brees just didn't/doesn't have the arm anymore to utilize Cooks