Public spending on infrastructure and services raises land values, as parks, police, and fire departments make locations more attractive to live in. This subsidizes landholders and allows them to charge higher rent whenever these services are paid for by a tax on labor rather than a tax on land.
With a land value tax, landholders have to privately invest in improving the private property on their land, such as expanding the supply of housing units, in order to increase their profits. Without a land value tax, landholders can earn greater rent and profit without actually privately investing in improving their property. They simply have to lobby for higher public spending paid for via taxes on income or consumption and then they can raise rents without competing to improve their supply.