Several no longer existing civilizations built out infrastructure that proved too complicated to maintain. So they had, for some time, "good employment numbers

Several no longer existing civilizations built out infrastructure that proved too complicated to maintain. So they had, for some time, "good employment numbers or infrastructure investment". Then they "were destroyed", or more often faded away as folks adapted, migrated, or died. Details can be scarce, as your stone carving artisans might simply stop making records. If there are any records. Some of these fallen civilizations had water-works that gave short term benefits, but eventually failed: the system became too complicated or too expensive to maintain, soil salinity grew, earthquakes cut the qanats, maybe there was a run of corrupt or incompetent leaders, wars and political unrest can complicate maintenance, or economic and trade changes can make a once profitable area irrelevant, and it's a pity about those changing rainfall patterns. "Strong Towns" does exist as something of an antidote to mindless "it doesn't matter" infrastructure spending, and has pointed out various problems of popping up yet more suburbs that lack the tax revenue for maintenance. Or perhaps civilizations, like flowers, are all about short term gain before they fade away?