I would argue it's the other way around. There are only 3 companies who can make modern x86 cores: Intel, AMD and VIA. Intel doesn't license the necessary patents to others (besides those 2) to allow them to make x86 cores. Anyone with enough money can buy an ARM architecture license though which allows making your own core. At least the following companies have at some point made their own cores or modified the ones provided by ARM : Digital, Intel, Marvel, Qualcomm, Samsung and more companies are working on new cores.