Probably colonialism is partly to blame; to justify colonialist policies, Europeans engaged in motivated reasoning exaggerating the technological advantages they did in fact possess over other cultures (many of them Neolithic, despite existing up to the present day), and using them to justify claims of superiority not merely material but also intellectual and genetic. (A modern form of this is making fun of flat-earthers, anti-vaxxers, creationists, Apollo conspiracy theorists, Juggalos, and 9/11 truthers, and occasionally engaging in more violent rhetoric toward them.) It's to be expected that such politically-motivated claims wouldn't hold up as our knowledge deepens.

There's also the issue that, as long as our research isn't too shoddy, it's sort of unidirectional. Once you have found an example of Neolithic groove joints or whatever, you've established that at least some people at the time could make groove joints, even if you didn't think they could before. Going in the other direction would require showing that the original research was Piltdown-Man-style fakery or something.