The NFL hasn't been able to make its mind up about what the perfect wide receiver should look like for the past few years, and despite some obvious success stories, wide receiver remains one of the positions with the highest bust rate in the draft.
Much of that comes from the gulf between college offenses and their NFL counterparts in terms of complexity and demands from a receiver. A player might have all the physical skills necessary to succeed at this level, but in college he was only ever asked to run two or three routes.
Depending on what offense he lands in at the NFL level, he could have the choice of two or three routes on any given play depending on how the defense lines up and reacts.
You can talk to a player pre-draft and get a handle on his ability to think and process information, but you're never going to be able to reliably project how he will handle the mental workload and understand the correct adjustments in the scheme until he's out there trying to do it.
Chad Johnson has had a career that at times flirted with the Hall of Fame, but he was completely unable to grasp the Patriots' playbook when he was brought over from Cincinnati.
Johnson is still physically able to play the game and often got open on the limited snaps he saw for New England, but the Pats couldn't trust him to make the right reads and get to the right spot at the right time, so his playing time was cut to almost nothing by the end of the season.
If it can happen to a player as great as Johnson has been, imagine how tough it is for college kids who ran even simpler offenses, and how tough it is to project whether they will be able to make the leap successfully.
With that in mind, there are still certain traits that you need to look for to find a viable receiver at this level, because the right guy can succeed despite lacking desired measurables.