The Green Bay Packers currently have eight wide receivers on their roster. Take Jamel Johnson and Ed Williams out of the mix and they have six guys who could easily be on the final roster and who have all seen game action for the team over the last two years. Jordy Nelson, Randall Cobb, Davante Adams, Ty Montgomery, Jeff Janis and Jared Abbrederis would all be reasonable keeps for the Packers as of today and barring any health issues.
Furthermore, keeping six receivers is a luxury and not always a given. Given the health situation of the Packers receivers over the last few seasons, they understandably and likely prefer to stack the position with additional options.