Sorry in advance for bringing AI into this but... this is context engineering in a nutshell. DRY and SoC really mess with an agent's ability to efficiently gather context. If you limit all layers of a feature into a small area (e.g. folder) it's much easier to work with. Vertical Slice Architecture is a good example of this too.
It's a good point though this is also what makes it easier for humans. I think most good abstractions hide unimportant details in order to make it easier to reason about and reduce the context but both the appropriate amount of context and what is an unimportant detail are not consistent between individual devs and don't have good metrics to measure their qualities.
