It's about the scheme and play design and this offensive staff just isn't good at it. Look at other teams top receivers. Andre Johnson is leading the league in catches, yet every defense knows that on passing plays he is the primary target, who else are they gonna throw to, yet he still gets receptions. Antonio Brown is second and every team knows Big Ben wants to get the ball to him and they still find a way. Josh Gordon, most fans couldn't even name another Browns WR and they have no running game, but still find ways to get him the ball. Pierre Garcon gets a ton of receptions, and again who else are they gonna throw to, that team doesn't have any other real threats. We all see highlights every week of guys like AJ Green, Jimmy Graham, Gronk etc. catching balls wide open and think how could the other team just leave them so open? Sure, some cases are they just plain out beat their man, but in a lot of cases it's their OC creating plays to get them those wide open looks.
All those guy have a ton of natural talent, but so does Dez. The difference is those teams have found ways to give their players an edge and utilize those talents.