Because it's marketed as AI and it takes a while to figure out that it's really quite limited. In my opinion there's not a lot of intelligence going on, It's great at translating a requirement and giving you an approximation of what you asked for, but there isn't really any "thinking" going on.
I think when they advertise "thinking" it just does a few more iterations of giving you the closest "number in your head from the clues you've given it (requirements).
I saw someone once say that LLMs are a kind of "word calculator" and I feel that's quite a good description.