I wish the mod did "this" because it's like that in real life.

[JamesNinelives]

Sarcasm aside, the reason maintenance in 4X/TBS games cost currency is an abstraction of having to supply your cities/units with the materials for them to maintain themselves, rather than allocating labor to do the repairs.

The "real life" equivalent is hiring private contractors/sub-contractors.

Or even just paying state-owned companies with money from the state treasury. Most work involves transfer of money at some level after all .