In lieu of understanding the whole architecture, they assume that there was intent behind the current choices... which is a good assumption on their training data where a human wrote it, and a terrible assumption when it's code that they themselves just spit out and forgot was their own idea.
Mediocrity in, mediocrity out.
I mean, DB schema versioning is one of the things that you can dismiss as "I won't need it" for a long time - until you do need it, at which point it will be a major pain to add.
> even though Memory.md has the AWS EC2 instance and instructions well defined
I will second that, despite the endless harping about the usefulness of CC, it's really not good at anything that hasn't been done to death a couple thousand times (in its training set, presumably). It looks great at first blush, but as soon as you start adding business-specific constraints or get into unique problems without prior art, the wheels fall off the thing very quickly and it tries to strongarm you back into common patterns.
I'm doing it right now, and tbh working on greenfield projects purely using AI is extremely token-hungry (constantly nudging the agent, for one) if you want actual code quality and not a bloated piece of garbage[1][2].