As has been stated, per his contract would cost the team almost as much to cut him as keep him. The Bills have 5 WR's active, they likely aren't going to go with 6, add to that Samuel doesn't play ST so he's the odd mad out.
If they do cut or trade him, what if someone gets hurt? It's not likely the team is going to pick up someone else as good as Samuel, plus then paying two guys.
The odds of going through entire year without one of the WR's missing a game or two is likely low, so it's a smart move to keep him. The Bills have a loaded roster, it's why they signed guys like Phillips, Poyer to PS if someone gets hurt, they have experienced players to back fill.