Also if you take 1 generation step back into the 2600 or intelivision there was a very simple API they did use that was built in. It was usually little more than fill out some memory in a particular way and flick an interrupt or particular instruction and it would either run something in bios or hardware. Also many did not need much in the way of an OS as they usually just either memory mapped themselves into the address space or copied themselves there. At that point if you keep your memory in order you do not need much and can toggle the registers yourself or call into bios routines yourself.

The newer machines use APIs to abstract. Where companies used to conform to particular HW standards (VGA,EGA,etc) with extensions. Now HW companies see their drivers as a differentiator. While the programmer writes to the abstraction API. Technically you could still write bare metal but few companies want to say what their real API looks like. So you are stuck with the OS or if you are lucky what someone else has noodled out.