It also works more reliably. I've tested this quite a bit. Instructions in files referenced via CLAUDE.md are more likely to fall out of context or to be ignored. Raw project level CLAUDE.md instructions are the second most durable available as far as I know. I used to have a "well organized" hierarchy of rules and instructions. Collapsing all of that into CLAUDE.md + skills made things far more predictable and "as instructed".