To see how the Intel CEO is thinking, I now scrolled through a few interviews with him.
In this interview, Intel's CEO is asked to describe the difference of a CPU and a GPU:
https://www.youtube.com/watch?v=d07wy5AK72E
His answer is that the CPU is capable of doing general computing, while a GPU is made for very specific tasks.
I'm not sure if that is a good way to put it.
The way I would put it is that a GPU is a bit like an array of many CPUs. And to manage this array of processors all doing computation at the same time brings constraints and management overhead. So it is usually harder to program a GPU but results in better performance.