Good question. I imagine for the silence and low power usage without needing huge amounts of storage. That said, I own an n100 dual 3.5 bay + m.2 mini PC that can function as a NAS or as anything and I think it's pretty neat for the price.
This sounds exactly like what I'm looking. Care to share the brand&model?
Noise is definitely an issue.
I have an 8 drive NAS running 7200 RPM drives, which is on a wall mounted shelf drilled into the studs.
On the other side of that wall is my home office.
I had to put the NAS on speaker springs [1] to not go crazy from the hum :)
[1] https://www.amazon.com.au/Nobsound-Aluminum-Isolation-Amplif...