This is true for any field, including medicine.

Specialists in, for example, psychiatry don't need to understand how mitosis works, etc...

The same is also true in finance. People who do model equity index volatility don't remember at all how to derive the equation for put-call parity.

In each of these fields there are people who study each of the fundamentals, and then there are people who do more routine "code monkey" work in a narrow area - think chiropractor or vanilla stock trade execution.

Programming is not unique.