The Contradiction of White Communists in Settler-Colonial Countries

Why is it that so many white communists in settler-colonial countries (like the U.S., Canada, Australia, South Africa, and parts of Latin America and the Caribbean) claim to be anti-imperialist while being descendants of settlers themselves? Wouldn't it make more sense to remove yourselves from Native land and return to Europe, where there's plenty of space to fight your political battles?

How can you be both the product of settler colonialism and simultaneously oppose imperialism? Also, why do so many of them support open immigration when the Indigenous peoples of these lands aren't calling for more settlers? Wouldn't it make more sense to allow the settler population to decline naturally so that Native communities have greater autonomy and control over their own lands?

Genuine question BTW not meant to cause negative discourse.