The census was for tax purposes. Making people move away from where they make a living makes no sense in that context.
You’re looking at it through a modern lens. Taxes at that time were levied against families. People were expected to pay as a privilege of Roman “protection”. It’s a little like Obamacare where you are taxed for being an American citizen.
Besides, it’s not like they were able to electronically track transactions. It’s a little like our government trying to get tax money out of cash transactions today... good luck!