That's not exactly true. The main advantage GPUs have is they are not general-purpose, they are accelerators. NVidia made GPGPU successful by saying "throw away your C/C++ code and use this entirely new language (more appropriate for the hardware) to program this thing", and backing that up with impressive performance improvements. Intel failed with Xeon Phi because, essentially, they promised you wouldn't have to rewrite your code to get the performance improvements, but the performance improvements were anemic if you didn't rewrite code.