Honestly post 2005 things did slow down dramatically for typical single core workloads.

In the late 90s and early 2000s the mantra was "why waste time optimizing your software? By the time you're done the next gen of CPUs will have made up the difference."

Now the increase is more about moving to GPUs and power efficiency etc. We still have increases, but the rate of speedup has slowed down a lot.