The motherboard manufacturer integrated the chipset into their board. They worked with Intel, or Intel's spec/API directly. They are responsible for your machine's interaction with the CPU.

The same is true of all the devices directly integrated into your motherboard. Broadcom/Intel wireless chipset, Ethernet, audio, etc.

It's a chip that your motherboard manufacturer hardwired in (e.g. part of the chipset). Firmware updates need to go through the efi/bios they set up