Concrete was mostly used in large building projects. These were expensive and thus usually sponsored by those wealthy enough to invest in such projects, particularly if they were vanity projects. In Rome, that would be the Emperors. Outside, it would typically take multiple sponsors.
The decline in economic stability around the Third Century, the reduction in profitable conquest due to military power being invested in civil wars of succession and the increasingly expensive bribes for the Praetorian Guard all contributed to Emperors having less money to spend on such projects, with predictable results: Less projects were built.
This is vaguely recited from an AskHistorians post, all errors are on me.
Actually, it’s not entirely disconnected.
Concrete was mostly used in large building projects. These were expensive and thus usually sponsored by those wealthy enough to invest in such projects, particularly if they were vanity projects. In Rome, that would be the Emperors. Outside, it would typically take multiple sponsors.
The decline in economic stability around the Third Century, the reduction in profitable conquest due to military power being invested in civil wars of succession and the increasingly expensive bribes for the Praetorian Guard all contributed to Emperors having less money to spend on such projects, with predictable results: Less projects were built.
This is vaguely recited from an AskHistorians post, all errors are on me.