I think that's part of it: one crucial component of the myth is "where is home" vs. "where is in exile," and so keeping "Egypt" in the myth would be counterproductive.
But another part of it may be that one is not allowed to speak of the mysteries, and so obscuring deities or mythic characters as historical or pseudo-historical people may have been a way of hiding the mysteries in plain sight, so to speak.
Another part of it is that what we Westerners think of "historical" is simply not how other societies or civilizations think. For example, Herodotus, Berossus, Manetho, Diodorus Siculus, etc., freely mix hearsay and myth in with what we would call history; this drives modern historians nuts (and there has been much ink spent on trying to tease apart "fact" from "fiction"), but perhaps that says more about us than it does about Herodotus.
no subject
But another part of it may be that one is not allowed to speak of the mysteries, and so obscuring deities or mythic characters as historical or pseudo-historical people may have been a way of hiding the mysteries in plain sight, so to speak.
Another part of it is that what we Westerners think of "historical" is simply not how other societies or civilizations think. For example, Herodotus, Berossus, Manetho, Diodorus Siculus, etc., freely mix hearsay and myth in with what we would call history; this drives modern historians nuts (and there has been much ink spent on trying to tease apart "fact" from "fiction"), but perhaps that says more about us than it does about Herodotus.