Steve Wozniak, the Steve that built the first Apple computers, knew what every component on it did, and he wrote every line of the ROM. Nowadays it's, "Well a Stackoverflow comment said if I add this line in the config, it will work, and it did, so... I closed the ticket.", but the complexity of computers nowadays makes it unfeasible to learn everything inside out, at least not if you need a gazillion developers (I think only a low low sub-percent of them know their software and hardware stacks inside out) because everything needs to be software-ized.