There is your explanation, it doesn't make sense form a gameplay standpoint nor from an historical one.
But it annoys me that for "gameplay", King Tiger and Jagdtigers were readily available and deployed everywhere. The Battle of the Bulge AKA battle of the heavy tank fetish.
Allied air "superiority" had been bombing strategic positions as well as keeping control of the sky, but the secret underground nazi super factories that are mass producing super heavy tanks cannot be stopped.
Besides, real tanks that were properly mass produced and performed well without large mechanical failures did all the work. I can design stereotypes without the drawbacks, too. :/