Your question frames their purpose as just making it more costly to live. The ideal reason is to cover the costs of services that are hard to limit to only payees, or ones whose cost benefit from economy of scale. The actual reason is to milk people for as much as they'll put up with, and exert control over people's actions via incentives (less tax if you do this or avoid that) and punishments (more tax if you do this or don't do that). A hidden tax is money printing, but this is unfocused because it takes the most money from people who are saving dollars, either in banks or under the mattress, or things whose prices can't keep up with the devaluation of money.