When you use frameworks or libraries, you are trusting (hoping) the author(s) spent the time to get it right. At a minimum, the framework/library is documented in literal documentation and/or code that's static and can be read and understood by you. Ask an LLM to do a task 3 times, you'll get 3 different outputs - they're non-deterministic.

I catch a lot of nonsensical and inefficient code when I have that "back and forth" described above - particularly when it comes to architectural decisions. An agent producing hundreds or thousands of lines of code, and making architectural decisions all in one-go will mean catching those problems will be vastly more challenging or impossible.

I've also found reviewing LLM generated code to be much more difficult and grueling than reviewing my own or another human's code. It's just a mental/brain drain. I've wasted so many hours wondering if I'm just dumb and missing something or not-understanding some code - only to later realize the LLM was on the fritz. Having little or no previous context to understand the code creates a "standing at the foot of Mt. Everest" feeling constantly, over and over.

False equivalency. The maintenance and expertise required to run the codebase you’ve generated still falls flatly on you. When you use a library or a framework it normally is domain experts that do that stuff.