After you beat the E4 and Champion, you become the new Champion. Story wise, it doesn't make sense the former Champion gets to hang out in the Champion's spot while you have to curb stomp the E4 again to get there.
They need to fix this problem.
You beat the Champion, but you are not ready to take on the demands and responsibility for the position. So you are given a key item that gives you special privileges as Champion and the Champion retains the title. Then each follow beating of the Champion, you get a rare item.
After X wins, the Champion gives you the title and you are confident enough to take on the position.
From that point onward, you are free to go to the champion area bypassing the E4 where a random trainer, Gym Leader, E4, or former champion challenge you for the title.
In addition, you can battle a clone of your last team that won the Championship. --- I reject your reality and substitute my own! I'm not a racist. I'm an optimist.