The problem with increasing productivity is that one consumption stops keeping up, it kicks off a bad spiral: spending/productity goes down labor income goes

The problem with increasing productivity is that one consumption stops keeping up, it kicks off a bad spiral: spending/productity goes down labor income goes down spending goes down (rich people save much more) spending/productivity goes down ... In principle, this can continue until the now-overkill old (physical) capital falls apart, and perhaps knowledge that went with it, and living amidst ruins, spending/productivity stabilizes again.