There are plenty of reasons.
Radiologists aren’t being replaced by AI because of liability. Same for e.g. civil engineers. Coders don’t have liability for shipping shit code. That makes switching to an AI that’s equally blameless easier.
Also, data: the web is first and foremost a lot of code. AI is getting good at coding first for good reason.
Finally, as OP says, the hard work in engineering is actually scoping requirements and then executing and iterating on that. Some of that is technical know-how. A lot is also political and social skills. Again, customers are okay with a vibe-coded website in a way most people are not with even support chatbots.
Depends on the industry, and shipping shit code is the reason cybersecurity laws are starting to be a thing.
What if you're shipping code for a therac-25?
If anyone doesn't think all of that is going to happen again on a massive scale as companies embrace GenAI, HAHAHAHAHAHAHA. AI will change a lot of things, but it won't fix human nature.
Yet another reason why this needs to change, fast.