> Most ARM CPUs are manufactured not by ARM itself but by Samsung, Qualcom, Texas Instruments and the like.

Not quite. With the exception of Samsung, those companies design ARM-based systems-on-a-chip, but do not manufacture them. They take an ARM core, perhaps modify it, add on a bunch of other stuff like graphics accelerators, memory controllers, ethernet MACs, and so on. Then once the design checks out, they send it to another company, like TSMC, UMC, or GlobalFoundries, that actually does the manufacturing.

The capital costs of building each new generation of chip fabs have grown tremendously, which led to this centralization and commoditization of chip manufacturing. Intel is one of the few holdouts, and they're usually a bit ahead of everybody else, which is one of their big competitive advantages.