Settler colonialism by nature requires very large numbers of participants. One of the key components is just squatting on land & driving people out. That takes a whole hell of a lot of people.
Enter the myth of "America" to soothe their cognitive dissonance & keep them from asking themselves "are we the baddies?"
Again, that's why we can't keep these myths. The myths exist to allow, facilitate, & erase the violence.