19th century archaeology and anthropology was
thoroughly racist. It was a time where explorers could rediscover something like Great Zimbabwe and go "We found the Lost Tribe of Israel" because there's no way that the native inhabitants living among the site could
possibly have built such an exquisite structure. It was a time where racism wasn't "dark-skinned people are bad" but rather "let me give you a lecture on how the physiology proves that these savages are incapable of reaching the higher thought patterns that are necessary for civilization to exist." It was also a time where Americans were the cultural backwater of the world, and the forefront of scientific racism were Europeans wandering around their empires, seeking greater justification for why they had to be the ones to rule over the lesser peoples.
It's only in the latter half of the 20th century that the field stops presupposing that Europeans are better than everybody else and they start trying to more objectively and holistically evaluate life in other societies and compare them. There's still a large contingent of popular anthropology that hasn't caught up to that memo yet, and the general field of pseudoarchaeology absolutely thrives on it.
There's a reason that people treat the methods of construction of the Pyramids as some unsolved mystery but not, say, the Colosseum. And it's not because we don't have the evidence for the Pyramids--we have the written records that discuss pyramid construction, we have the letters from the Pharoah complaining about his workforce!