It is fairly common for a governmental entity to rent land at a nominal fee (usually $1.00 a year) when the community (including its politicians) wants to give a conspicuous location in the public square to an organization.
Even if the Scouts decided to pay the rent, this is just the beginning of the effort to drive them out.
Personally, I hope they either demolish the building or take it apart and relocate it to a piece of land (outside of Philadelphia) that they own.
If it ain’t on wheels, it belongs to the landholder as a fixed capital improvement.