How long should a loading spinner take to do one rotation?

Whilst I'd always prefer an estimated time, I get that's not always possible, so we fall back to the tried and personally hated, loading spinner.

I've always thought that having it do one iteration every second was super helpful. It provided an frame of relativity for measuring loading times. Although as I write that I'm thinking I know the answer, but let's try anyway:

How to decide on a speed for the iteration of a loading spinner, and why is a set default like 1 second not seemingly the norm?