Ask HN: A Laptop that outsources processing to a Desktop?

Why does not this exist? A laptop that just contains a display, a keyboard and a mouse/trackpad, that just take input and send them to desktop and just display what the desktop broadcasts? I have a powerful desktop at home, but I don't want to spend all day sitting in front of it. If I have such a device, I can work from anywhere in my home. And it would not fry my lap like a cheap laptop do...

The way I see it, if you are living in a hot country, the actual machine does not even need to be inside your home, heating your rooms...

Why does not this exist?