The difficulty comes from meeting the exact requirements and providing a reliable result. Would you be so sure of this opinion if the requirement was to write "a simple CRUD app", but it had to integrate with a poorly documented legacy system and was for a big client with an SLA that could sink the business? Many devs find themselves in that exact situation all the time. What you end up writing, with AI no less, is tomorrow's poorly documented legacy system.
You don't know what you don't know. I'm reminded of stories where people from Europe traveled to America and underestimated how massive it is. They thought "just a few 5 hour roadtrips" sounded relaxing. They overlooked the details and found themselves falling asleep at the wheel, thirsty/hungry, and backtracking for hours.