Its to allow you to easily move by shipping your pod with all of your stuff in it, no need to do as much packing/unpacking. Pretty much the only thing to move would be to secure breakables then lock your cabinets shut.
This would make it easier to change employers as you only need to see if a potential employer has open rack space nearby, rather than dealing with possibly selling/buying a house or finding a suitable apartment nearby.
I find the appeal similar to the containerization technologies for computer software that have taken off recently. While having the binaries as part of the container is nice, the important part is that I can put my containers pretty much anywhere with minimal effort on my part and quickly/easily move if the current host tries charging too much. This basically is trying to do the same for housing.
Also you are not locked into the whims of the developers of the racks as much as you are with an apartment. Like making lots of noise at 3AM? Buy a pod with lots of sound insulation, same goes for someone who works night-shift and wants to sleep at 6PM on Saturday when everyone else is having a party.
This would make it easier to change employers as you only need to see if a potential employer has open rack space nearby, rather than dealing with possibly selling/buying a house or finding a suitable apartment nearby.