Take Kennedy as an example he made himself a star.
Kennedy is not a star, nor is he a self made one. The WWE pushed the hell out of him on SD, once he got to Raw and he was basically on his own, he flopped.
Most of the industries biggest stars are stars because they had a quality the fans liked about them. This is a combination of natural abilty, hard work, timing, gimmick, storyline, and company push.
You can give a no talent hack a decent push and he won't become a star based on that gimmick/push along. They need a certain factor that sets them apart and makes the fans care about them.
I will use the Rock as an example. He was given a generic rookie face gimmick. The crowd wanted to kill him. He didn't get the correct reaction, but the fans cared so much they gave him a huge reaction. the WWE changed his gimmick, turned him heel and a star was born.
Then there is poor Cody Rhodes. Same gimmick as the Rock. Comes out to nothing. The crowd doesn't care about him.
The Rock had an innate quality that made him great, but without the proper push he wouldn't be able to take advantage of that quality. The WWE has the responsibilty of recognizing when someone has talent.