Because people don't turn "corners" in that amount of time. Gordon and Blackmon turned corners too. Where are they? What's Chris Carter's up to too? Or Greg Olsen's brother? They turned corners too. Hell, so did Burfict.
Shut the fug up with that poo. It's as generic as "I wanna thank god...". A small of percentage people change in that amount of time. Cook hasn't changed. He just hired good representation.