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!
No, I’m looking at it through the lens of what we know about censuses of the time (a lot) and common sense. If the state wanted to know the tax base of an area, they sent tax/census workers to people’s homes to establish what they owned and what they did.
Having everyone move around the country to places where they don’t live or work is a recipe for a tax disaster. There’s no record of any Roman tax census requiring people to do such a thing and for very good r.easons