The mobile design isn't puzzling at all. It's infuriating, but easy to see why they're doing it. They want to force everyone onto the app because it's easier for them to advertise on.
And easier to monitor and track all aspects of a person privacy such as precise location, altitude, Wifi ID, device type and characteristics, screen size, and so on.
Also people are easier to track if they use the app.
Not arguing with that, but why they still allow 3rd party clients then?
I don't see them closing down their public api. It's pretty hard to police such things when you have one.