Why can't you go into the imperial gaurd places even though you are know as the Champion and still can't be in guard bartracks and stuff like that?

do you mean champion of the arena?

Because thats how it is no matter what you do they wont allow it but on some occasions the guards don't ask me to leave at all!!!

If you mean the Imperial Palace and the other areas like Ocato's room you have to do the Theives Guild quest but if you mean the reagular Barracks then idk but you can illigaly ^_^

I think because the politics of the monarchy,the kings or Septims are at the topo, início so they have the
ability to use the whole tower floor 1-5,Ocato 1-3,you 1-2.

because you are just a fighter not a guard

I dont know probably its A glitch or something xD