When the government gave or sold the land to the first titleholder, it was not giving or selling absolute rights over the land – that is sovereignity, which governments usually don't sell or give up (although occasionally they do, e.g. Russia selling Alaska to the US) – it was giving or selling only partial rights. Even if it labelled the transaction "freehold", I think in reality all real estate is actually leasehold, with the government as the landlord, subject to lease conditions (laws) and rent due (taxation). It retained the ultimate ownership of the land, and only sold/gave a limited and subordinated form of ownership.

Suppose someone wants to lease land, and make the rent proportional to the tenant's income. You might think it is an odd arrangement, but freedom of contract implies if landlord and tenant agree on this it is binding. Now, that essentially describes income tax. The government owns all its territory, it has leased it to the residents of that territory, it has made the rent (tax) proportional to income. If you don't pay your rent, the government can seize your moveable property, just like how your landlord can seize your moveable property if you don't pay your rent. (Unpaid rent is a debt, and its collection can be compelled through the same legal processes as any other debt.)