It's nice not to have to listen to your neighbours through the walls

They're easy to manufacture and move into place and remove if theres problems(pests, fire, etc). Depending on how he selects people a lot of the unhoused population are not mentally well and/or have substance abuse problems. This means if someone is a hoarder or sets their own place on fire it is not as consequential to their neighbors. It also is less likely to cause problems with neighbors if you have just a little bit of room. I would imagine for something like this to thrive you would want to build community and if people are annoyed with their neighbors because they are sharing a wall it would cause problems. I don't know the real reason just throwing out ideas.