It can possibly be because that is what history is. It is the study of things which are not the present.
It is irrelevant whether yesterday is like today because history is not about yesterday. Again, if you are interested about this subject, I would read some books about historiography (EH Carr and Elton are two of the most important books of this last hundred years...but, again, I don't think you will find anyone arguing for the position you are taking because it so clearly is an attempt to justify a political position today...this isn't what history is, any political position today has to be justified in the terms of today...historical relativists do not take your line, no-one does, it makes no sense unless you have no idea what history is).