This thought came to me while watching an Australian reality show (of all things) and my second caveat is that this is very anecdotally driven from my side. But I've realised that I've never seen Australian Aboriginal people feature much in Australian TV programming. Doing a bit more digging, the Australian parliament is largely made up of European-looking faces (from my very quick glance through the first 96 results). The demographic looks similar for the US congress.
Contrast this to my country's parliament's members, South Africa there's more of a mix of European and African. India's is largely made up of Indians.
I assume the answer is that this is simply the demographic makeup of these countries (wiki on Aus demographics, USA and RSAhttps://en.wikipedia.org/wiki/Ethnic_groups_in_South_Africa), so then my question is why are the demographics to skewed to Europeans in these two nations (there may be others I am missing) as opposed to other colonised nations? My assumption without having done more research is that many more colonists just went over to these two places compared to others, but is there more to this than that? (Also, to be clear, I'm not looking just at representation in politics, that's really just a big convenient list of people, but in more general spheres)
I am sure someone more knowledgeable will give you a plethora of reasons; in the meantime here is some reading on the genocides of Aboriginal and Native Americans from this sub:
Eta: there are good links within each of these posts pertaining to the significant loss of life in the colonization of both places
Europeans, Asians and Africans all being interconnected by land, had developed immunity to diseases like small pox which originated in the African continent. However isolated people groups such as the Aboriginal people of Australia, America and Polynesia hadn't had any exposure to the disease so they were really vulnerable. Also imperialism, racism and colonialism.