Two kinds of processor, two kinds of work
The general-purpose processor in a computer is built to do a small number of things very quickly, one after another. The graphics processor is built to do an enormous number of simple things simultaneously, which is why it was originally for rendering images and why it turned out to be exactly what machine learning needed.
That difference explains why one company's graphics hardware became central to the recent machine learning boom, and it is worth knowing which company that is.