Why are people online so extremely and blatantly racist towards indigenous people

Im posting here bc i cant post in the Australia thread (and I also lwk need to vent) but genuinely why? Racism as a whole makes no sense. So earlier today i saw a video saying "one of your ancestors lived like this btw" and it was photos similar to what it looked like in 1800 Europe i saw other comments similar and so I commented "well im aboriginal" and thruout the whole day today ive been getting commented after comment saying that im "mixed" and im not black and it rly pisses me off bc how can u look at a person alone and say "they're not aboriginal" i have shown up in community since I could remember not to mention it actually know my mob and who's family. I get its just the internet and not to take it to heart but i feel like its a shitty excuse for racist behaviour and im sick and tired of keyboard warriors thinking they can get away with it.