Using a library keeps the context window smaller than writing it all yourself. I also suspect the whole vibe-coding thing works best when most of the total running code is NOT vibe-coded, and follows carefully defined behavior the fast-and-loose parts can build on top of.

Otherwise, why bother to run your vibe-coded website on nginx? Just have the LLM spit out its own novel web server, its own novel TCP stack, its own novel OS for that matter.