Comment by burnt-resistor

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.