This is less true now than it once was, but one of the things Apple used to be good at is producing a new OS for the last generation of hardware that made it faster. Most manufacturers unerringly make the old hardware slower.
There's an old trick in software development, some of us learn it by example, others by experience: be conservative when rolling out performance improvements. If you have a feature you know will make things slower, pair it with changes to improve performance. If you make version 1.2 faster, and version 1.3 is as slow as 1.1, people will feel robbed (because performance is a feature and you just removed a new feature).
Pulling this off can be problematic unless you happen to work on both features. What if one slips to the next release? One of the perks of being a generalist and having some seniority is that you have a degree of control over such things, where others might not.
If Apple had wedded the clock throttling to a new major revision of the OS, people would hardly have noticed.