Right now, as we speak a lot of agents are doing clunky things to operate websites from Codex to Claude, all those website owners might not have the resources to setup an MCP or API just for agents. If this was an exceptional case how come Claude and Codex are still operating websites using clunk embedded web browsers and headless chrome complications.
It would take a lot to setup an API for certain resources when you consider stuff from security to compliance, but if you could just slap on a React plugin on already existing UIs so now agents can use the same site as humans already do.