If you add all those .md files to your AGENTS.md, your harness will likely load all those files into context. This will create context pollution for you.

Context, similar to your computer's memory, is limited.

Additionally, the more things the AI has in context, the worse it performs.

Skills helps you to quickly add more context for doing things, without polluting your context window.

I think you need to learn about AI, there isn't anything hype there. It's just an easier way of giving more context to the AI.

This can be helpful, for example, if you have an internal API that does XYZ, and you want the AI to know that API, you can save that API, its endpoints and authenticaiton methods to a skill, and invoke it when you want your harness (CC, Codex) to know about the existance of that API, to make requests, make tests etc.