Anecdotally, the reason my career is in embedded software is that I kept wanting to know how the (software) system works, and embedded is as deep as you can get without changing disciplines altogether.

The cost is you lose those layers of abstractions you get at the higher software levels, and there's only so much complexity I can handle.

(the funny part is that even HW registers and stuff are just an API that the hardware chooses to expose. As Alan Kay said: "Hardware is really just software crystallized early")