Well as someone who does buy PC fans, let me tell you that Noctua is clearly superior. It may be just a plastic fan with some bearings, but it doesn't seem to be easily replicable because nobody has managed to do it.

And it’s quieter than many of its counterparts from other vendors. And it actually doesn’t cost that much - more expensive than cheap-o versions for sure, but then again significantly quieter, that’s their whole premise.

The devil is in the details. Noise, static pressure efficiency, reliability, bearing quality, motor quality. Yes, there's a huge brand premium too. For critical uses, using a crap fan is an absolutely stupid decision especially where damage or malfunction is likely.

In zie olden PC days™, there weren't many options for quality fans except maybe whatever random fans Delta made that generally weren't optimized for low noise or low power consumption. Ancient, no name sleeve bearing fans would almost always go out within 1-2 years at 24/7 100% duty cycle.

Almost everything you buy "does not cost that much", that's how companyies make money.