Football is the most interdependent sport, as the success of one player rests more on those around him than in any other athletic endeavor. Within that, receivers are as dependent on the forces around them as any players on the gridiron.
Say you come out of college and you have all the tools to succeed. You're a height/weight/speed guy. A scout's dream. In the right offense, you have Rookie of the Year potential. Now, imagine the following two scenarios.
In the first you're drafted by a team with a brilliant head coach, a staff of bright offensive minds, a stellar quarterback and an established group of receivers who will help you stay open by demanding more coverage.