Why Erasing History Isn’t What You Want (not even as a dictator)
Your faith or cultural or national tradition depends on it existing in an ecosystem of other faiths, cultures, and nations. How, for example, will you explain to the youth that you cast out the idols, if there are no idols that anyone can find from that period?
More generally, if you erase the tragic history that you are trying to reject, then no one has any reason to believe that it ever existed, which means you are insisting on behavior and practices without any reason at all. You just come off as irrational jerks.
If instead you erase the golden ages of the past, thinking that you can portray yourself as the best alternative, you remove hope for improvement in the current situation, and hence the nation will suffer from despair and generally behave in savage ways, when you probably wanted the people to be docile.
If you merely erase the history, then either you have branded yourselves as counterproductive idiots (for reasons previously mentioned), or as wanton pillagers. Furthermore, seeing that the history does not exist, the population only can assume that either the current regime is engaged in such idiotic practice, or that there were obvious catastrophes in the past, in which the founders of the current regime participated. Neither assumption benefits the current rulers.
If you manufacture the history, you add (on top of the problems you create by erasing the history) that the current rulers are so insecure in their position that they actively have to deceive the population in order to persuade them to obey.