Cuts into James Cook opportunities to develop into lead back
The biggest reason for the Buffalo Bills not adding Dalvin Cook is because of the impact it would have on the development of his brother James Cook. The Bills drafted Cook in the second round last year and he spent most of the season behind Devin Singletary on the depth chart.
The Bills would see Devin Singletary leave in free agency and sign with the Houston Texans. This clears the path for Cook to be the lead back and get likely over 15 touches per game between the rushing and receiving work out of the backfield.
The addition of Damien Harris is the perfect compliment to James Cook because he is almost exclusively a running back and not much of a threat out of the backfield. The 50+ targets that went to Singletary the past three years should now go directly to Cook and set him up for over 70 targets a game.
If the Bills were to add Dalvin Cook, he likely replaces his brother as the lead back and is more well-rounded as a receiver and running back. The Buffalo Bills are going to remain a passing offense and while Dalvin Cook could still be effective in the right situation, the Bills should stick with the group they have on the roster.