Because the government needs to know who you are to do anything involving you. Taxes, drivers' licenses, passports, courts, etc.
I'm not arguing we don't need a government. But to silently take for granted that everything from income taxes to public roads and travel restrictions are a given jumps ahead here.
We could decide, for example, that the government shouldn't be allowed to centralize certain data and remove some of what we expect them to do instead.
How exactly government manages our data is a valid concern and in the modern world this needs to be reevaluated.
It would be good to clamp down on private companies collecting that data.