There are guys who were made to be champions. Unfortunately for us, Vince McMahon is the guy that gives the word on who will be champion.
If you jump ship and return (Christian and Gail Kim), you will be screwed out of any opportunity of a title.
Then there are guys like HHH and Batista, who get ridiculous amounts of title shots (not that they are not deserved or anything).
Finally, there are those that had the ability to become champion but left WWE for some reason or another.
I made a list of five guys that I believe had the skills to eventually become WWE or World Heavyweight champion but are no longer with WWE.