You trust machine code because it was produced by a deterministic system that was written and tested thoroughly by other engineers.

AI systems are not the same. You can't guarantee deterministic output.

Also, code is still the best language we have to convey our intentions as engineers into function. Natural language is too imprecise and ambiguous.

Understanding the code allows us to understand the intention behind the code and identify bugs, plan and architect better. Inspecting prompts gives you a blinkered view of the system meaning you're more likely to make incorrect assumptions leading to serious bugs.