Slot receiver scared and cant catch the ball

Why is it that as soon as a receiver or tight end gets put in the slot position they become stupid and scared and all of a sudden forgets how to catch the ball? This is ridiculous. No matter what level the receiver is they become as good as starter receivers. Michael Irvin(98) is not someone who is afraid to go across the middle and make a catch. Neither is Gronk(96). I think its ridiculous that automatically the slot player is a little * about making plays. You guys need to fix that. Its unfair to only be able to have 3 valid options when there are  4 receivers on the field since the chances the slot makes a play are diminished so much. 

Why not make a slot receiver position so player actually go across the middle to make plays instead of playing like little *.