It probably depends on what they are aiming at:
The main purpose of this video was brainstorming. Having more footage was only a side product. That's why they didn't produce a more polished video.
They could, but it probably would have slowed down the process, because they had to spend more time adjusting the cameras.
Doing a multi camera live stream can get quite difficult to have every camera in focus, aimed at the right spot and arrange/switch the best cameras without covering some important part of the background image.
One impressive example of a multi camera video setup is Micah Scott 's Youtube channel:
https://www.youtube.com/user/micahjd/videosShe uses at least 4 cameras (one fixed camera, a DSLR for closeup, a microscope and one camera for her cat). In addition to that she also has a wireless camera, a camera in her mill and 3D printer and several HDMI capture devices for scopes or PCs.
She started a couple of month ago doing live streaming and is constanly improving the setup.