I have a table in the back seat of my car on each side. It is actually pretty awesome.
Why is it not in most cars?
Because auto manufacturers look for ways to cut costs and make cars so they leave the assembly line and end up on the dealership lots quicker. They do not add in additional features into the vehicle that would take time to be hand crafted for the passenger. Plus, most of the people who buy luxury cars do not sit in the back of their vehicles, even in the longer wheel based top of the line BMW, Mercedes and Lexus, even though that is what the longer wheel base is specifically designed for.
In other words, it cuts into the bottom line.
Orginally posted on Quora.