Externalities do, such as colonies or environment or mines or resources.

Efficiency is not a one way street. You need people with will and knowledge to operate the machinery or further research. Otherwise you will inevitably be eclipsed.

Recent lessons happened to Great Britain (colonies), Europe (know how and funding, war devastation), Ming China (complacency and bureaucracy), Japanese tech dominance (population got old and crammed in), Soviets (political pressure and mismanagement). It is happening to USA right now.

They stop exponential growth, and that's a good thing in the end.