If you connect the dots of the earlier MCP Client/Server docs you understand that your desktop AI tool was also a MCP Server. This MCP Server provided the tools like "search files", "alter files", "open file".

It's was simpler to design/implement the AI tool if these interactions had state. When this was generalized to internet interactions this no longer made sense and was gradually cleaned up.

I think at the same time, the AI tool "protocol" to interact with the local system moved away from MCP model.