The operating systems have plenty of knowledge about how CPU power management works. They are hampered somewhat by how things like Turbo Boost are implemented in a backwards-compatible way through ACPI P-states that can't directly convey this information, but it's still pretty straightforward for an OS to support even more complicated schemes like ARM's big.LITTLE.

The real problem is that the OS seldom has enough information about the software workload to know whether it is better run on all cores, or just a few at higher clocks. It falls to application developers to not spawn more worker threads than are necessary.