[dijksterhuis]

In a Venn diagram, "not leaseholders" will be all other space on the diagram.

I imagine it's meant to leave all other options on the table (taxpayers, developers and/or anyone else) rather than force a specific choice (except leaseholders).

[lmm]

If you legislate that it's not X and it's not Y and it's not Z, pretty soon it's no-one. Legislating that it can't be X is de facto making it the taxpayers' responsibility (or else permitting it to not be done at all).