There seems to be confusion here. People seem to be getting this backwards
Setup time, like hold time, DOES NOT depend on frequency. Setup time is nothing more than the minimum time requirement that data must be stable before the clock edge. That's it. It has NOTHING to do with the previous clock edge.
However, from a system point of view both setup and hold time, along with propagation delays, will figure into maximum frequency limits.
The original question was why doesn't hold time depend on frequency; it was not a question about overall system timing.
Said another way, frequency depends on setup and hold time; setup and hold time do not depend on frequency.