I am assuming they couldn't find and better option at QB last season. So maybe they figured with a one year and out QB, they would wait until the QB situation was more stable/long term to build the offense up.
Unless something was said by one of the coaches, I am not sure about the "all the catches" DiMarco was supposed to have, his career high was 13 and that was his only double digit reception year.
Tolbert was a waste on the field, but a great locker room guy that McD was familiar with. For a new head coach, those types of players are important in year one.
Benjamin will be good next season, but they do need to find a deep threat to open up the middle of the field for him.
I am really not concerned about their ability to build up the offense at all now that Dennison is gone...