At present, some of the cpus used by MAC are also used by Windows. Why not use AMD cpus when Apple is not able to independently develop chips?
In fact, Apple had been working on migrating operating systems and applications to x86-64 for more than two years, using devices provided by AMD, and AMD sent engineers to Work with Apple. The software on the Mac will have to be optimized for AMD processors, which will have performance and compatibility issues in a short period of time, and PC sales are not as large as mobile phones, so customizing the CPU is not worth it. Customizing the CPU means getting on board.
Apple's x86 project started in 2005, and IN the CPU market, AMD has been almost even with Intel since thunderbird in 2000. Moreover, when the Turadin Ben 3 retired, I can say that the military power of AMD to take the lead.
Most of the AMD300, 400 series motherboards have its corresponding design basically the same Intel motherboard, so it saves the motherboard research and development costs, and the problem is that most of the BIOS functions are optimized for Intel, so the AMD300 series motherboards just came to market when there are various holes.
The wholesale price of Intel cpus is considerably higher than that of AMD, but remember that apple also uses Intel Thunderbolt3 chips, and the overall cost of the solution may be close to that of AMD. Apple, as a manufacturer of not only products but also systems, did not want to add unnecessary work, so it only used Intel cpus.