Why dont historians interpret history the same way?

Because we rarely always  interpret anything the same way; or at least not unless ALL the information is available.

But history involves people and their thoughts and intentions; and this can never really be known (unless we can read minds): historians can't really know what someone's motivations were for sure, specially when that person is not opened about the motivations.

So you know what happened and so it doesn’t repeat it’s self

An informal structure in a bureaucracy would be something like so-called "office politics". where there's a formal structure set up for the organization, but then an informal subculture as well that has a way of organizing the bureaucracy further. this can be positive because it sets up an added degree of organization, albeit informal, within the bureaucracy.