In my case it does spin down, but nowhere near the acceptable level (It's in the attic, but I can hear it from any corner of the house)
These are
very high end, compact pieces of hardware. Just because you can buy them for peanuts today, doesn't take that away.
They were designed to run constantly,
consistently at full performance in a data center "like" environment. Noise is probably not even something that the designers focussed on, and was probably an afterthought. They are very sensitive to temperature, airflow, humidity etc etc and will do whatever is necassary to keep the switch within it's parameters.
I can almost promise you that if you move the switch into a different location with a different airflow, temperature (cooler) mix, the switch fans will ramp down and stay ramped down. Are the ramped down fans "quiet"? Not even close. But are they bearable? That again depends on the location.
My rack at home is in one corner of the basement, which is walled off from the rest of the basement (it's the unfinished part). This is probably the coolest location in my house, without building out a dedicated server room with it's own cooling. I can make the switch change fan speeds (in a few minutes) by just leaving a door open or closed...
That's how sensitive they are.