ARM designs the Core

STM, NXP, Mediatek, etc buy the core design, slap it on a piece of silicon, design peripherals around it (SATA ports, UARTS, SDIO controllers, etc), slap those on the silicon, put interconnects in between, and sell the complete SoC.

This is of course EXTREMELY oversimplified. But the idea is the same: ARM makes the CORE, and others make SoCs out of it. (I am not aware of anyplace you can buy a simple ARM CORE without it being part of an SOC.