Jesus fucking Christ you're on a restaurant booking page looking at a date picker and you need an agent to fill it out for you?
Seems obvious why an API would be helpful on that page instead of having the AI attempt to navigate the page, open up a date picker and click all around..
And as others have said, if you are disabled in some way being able to just speak and get something like this done seems pretty life changing.
But you go ahead and be mad about an api...
Sometimes it helps to not think of why we should reject things but instead to think of why someone might accept them.
If a page has good accessibility an agent should have no problem to interact with it. If WebMCP becomes an acceptable solution for accessibility then the only way people who need accessibility will be able to interact with services is via agents.