ELI5 the value a “prompt engineer” provides

not done much digging, but my naive understanding is that a "prompt engineer" crafts statements which, when used with a user's input, elicits a more accurate/desirable result from whatever model they're interfacing with.

Assuming that's the case, how is that role not BTFO by shifting that responsibility to the model by tuning it better(?) to return the desired response from a naive input, or by requiring the user to craft the higher-quality prompts themselves (probably not desirable.)

The few sources I've come across appear more hand-wavey than anything, would appreciate some technical insight if possible.