So that common services (eg. healthcare in Canada, education everywhere, roads) can be collectively paid for.
- why even work? Can't we just print enough money for everyone and live happily ever after?
Because there wouldn't be enough resources. (Fiat) currency is just a medium of exchange for real stuff. Instead of growing wheat and trading it for your wooden furniture, the state provides a medium of exchange so we can both just transact in money. eg. when I don't need more furniture but you still need wheat.
Money =/= wealth