You can't just look at it like that with that simplistic of a view. I think Dez is a hell of a player but there are quite a few games where you forget he is even on the team. It's been like that quite a bit in his career.
One of the main knocks on him is how with his size he has, he lets defenders consistently take him out of the play as they come to press him and someone his size should not have to fight that hard to get into his route.
Maybe he wasn't targeted because he was not getting open?
And yes, Garrett's schemes are bad. I know Linehan is now calling the plays but it's still Garrett's playbook. We are the most unimaginative offense out there when it comes to moving guys around. Dez is always out wide. Bring him in the slot sometimes. Put him in motion. Too many long developing routes from this team.