"Just automate it through the UI" sounds simple until you're the one maintaining that integration. When an API is missing, incomplete, or unsuitable for a task, an agent can often operate through the visible interface instead, the same DOM, accessibility tree, or screen pixels a person would use. That's a real capability. It's also a different engineering problem than an API integration, not an easier one.
The interface as integration layer
An API is built for software-to-software communication: defined actions, structured data, predictable error responses. Strip that away and an agent has to work with whatever's actually on screen:
A web page's DOM and browser state
An accessibility tree exposing control names, roles, and values
