Because it seems like tougher real-world technical problems (where there are tons of dependencies with other systems in addition to technical and business requirements) needs for the dev to have an understanding of how things work, and if you rely on an LLM, you may not gain enough of an understanding of what's going on to solve problems like this...
... Although, I could see how devs that are more focused on application development and knowing the business domain is their key skill, wouldn't need to have as strong an understanding of the technical (no judgement here, have been in this role myself at times).