An economy does not need mass demand.

It can easily reorient itself (and arguably, already has) to serving the demand of a small minority of asset owners rather than the majority of people. E.g. people building luxury yachts and working to maintain them, working in luxury restaurants, maintaining luxury gardens etc. instead of working in roles that improve the lives of the majority.

Because most people are working on things that improve the lives of the asset-owning minority and not of the majority, the standard of living of the majority is not improved, they have to work more for less.

How many high-paying jobs today actually do anything that benefits the 'common man'?