The laws of physics are intruding. Clock rate doubling without prohibitive cost, power, and heat have gone. At 3 GHz electrons don't go very far in 1/3rd of a NS. Chips are getting physically bigger (look at the Epyc). Easy increases in IPC are gone. There's an embarrassing number of transistors available, but few uses for them actually increase performance on things consumers care about.

Even GPUs are starting to peter out with lengthening product cycles, smaller improvements, and the increasing tendency to just rename the previous generation with a new name, as if it was actually significantly improved.

So CPUs have peaked, most of the low hanging fruit has already been taken. Most easily shown by pretty much all the popular CPUs from the previous generation maxed out at 95 watts or so (desktop or server), but are at 180 watts in the current generation. This happened years ago for desktops, but is hitting laptops (last year), and smart phones (this year or so).

GPUs are about half way there, improvements are harder. No more annual updates with 2x the performance on most common use cases. Feature improvements are getting more obscure, gaming sites are using 16x zoom to show the improvements. GTX1170 is rumored to be 50% faster than the GTX1070... from 2 years ago.

Specific use ASICs for mining, AI, and similarly narrow use cases are still early in their development. Multiple vendors are showing 2x improvements with each generation, even crazy things like including said chips in consumer devices with tiny power budgets.

So basically a core twice as fast isn't happening, it's not because anyone is lazy. There's tons of room for improvement in specific use cases where today's silicon is crazy inefficient. Things like machine learning, software device radios, vision specific processing, and related are seeing rapid improvements.