Somewhen in the last decades the decision has been made that the majority of gains should go to the top earners.
An easy way for demand to rise would be if wages didn't stagnate but went up with productivity. The top earners won't spend more money if you give them more. And new products won't be bought if no one can afford them.
Is this really feasible in a globalized economy? If wages were constantly forced higher wouldn't companies simply offshore increasing amounts of their labor or headquarter in another country?
I don't know how you could enforce this. But as I wrote before, as long as the elite keeps capturing all gains from productivity for themselves, demand will stay low.
Maybe there are tax schemes that encourage paying higher wages but I don't know.
An easy way for demand to rise would be if wages didn't stagnate but went up with productivity. The top earners won't spend more money if you give them more. And new products won't be bought if no one can afford them.