Actually not true. Perhaps surprisingly, CPUs and GPUs are progressing at about the same rate if you look at the high end. GPUs are all about massive parallelism, and if you compare against high end Xeons, the CPU core count increases plus things like AVX512 & FMA means they have been scaling similarly to GPUs over the past 10 years or so.

Nice analysis here (URL says 2013 but he has updated his numbers to end-2016). Looking at the graphs, you might even conclude that CPUs are improving faster in some respects.

https://www.karlrupp.net/2013/06/cpu-gpu-and-mic-hardware-ch...

Moore's law is about constant doubling times of number of affordable transistors in semiconductor photolithography.

GPUs are obviously subject to that, especially if you look at the affordable part.

Moore's law scaling has been over for about three years, few people noticed.