Because Rodgers wants to fully trust a guy and not take chances...
Plus Rodgers deep balls to guys with great speed has just been bad... yeah, he can throw the ball anywhere... but he almost never seem to time the ball up with MVS' speed... and while yes we have seen it this year, it hasn't happened too often with Watson and Watkins...
Also, Watson has some serious wheels, getting doubled teamed and sometimes burning them both, but used as a decoy instead of a ball actually being thrown to him.
But the Rodgers / Doubs chemistry looks like it could potentially be money ..