Replacement theology isn't just a Jewish thing, there are many groups who try to hijack another groups identity because they are ashamed of their own past or failure as a individual so it helps them elevate themselves above others to try to claim the past of another group they admire.
This is why you see so many groups try to pretend to be Israelites because they want the glory of those civilizations, some people do it for other reasons, in the case of the cult groups as the black hebrew israelites, they attempt to do so to grasp that feeling of victimhood as they legitimately believe they fit the curses of deuteronomy. Of course they have no proof of this, do not speak a semitic language nor carry any of the genetic traits of being a Israelite (most will claim DNA is a lie anyways). Other cults try to associate themselves as Israelites for various reasons. Jews aren't the only ones dealing with this issue.
It's kind of similar how people of pure European blood, or African American blood try to claim they are Cherokee Indians when they have no proof and most are doing it for attention.
Just ignore them and pity them.