Having a dedicated spec makes it easier for MCP client apps to implement some nice features out of the LLM loop (e.g. OAuth flow or elicitation ), some handy user facing features (e.g. prompts and resource), and some more advanced use-cases (like server sent notifications).

But yeah, a lot of it (including tools) maps well to HTTP semantics. In fact, at work we implement our features as HTTP APIs, and we’ve built a framework that exposes them as MCP servers.