I imagine its insanely difficult to write an automated status dashboard since a problem can cause the service to not work while not having everything entirely broken.
The apis tested by the automated system could all still be working. Probably the only way would be to have a constantly running vm testing everything via the web ui.
It's not that difficult, just a piece of work. Google has teams dedicated to just that kind of work and internally has the automated dashboards that update real-time. The confusion here is that the page linked is not it. This is some static HTML or such that is updated when a human has triaged the issue, determined and aggregated scope and got an OK from another human (or more, depending on the situation).
The apis tested by the automated system could all still be working. Probably the only way would be to have a constantly running vm testing everything via the web ui.