Even more generally you need the elite strata within society to actually lead and promote high culture with a sense of noblesse oblige rather than optimize everything for just satiating the base desires of the masses (the middle class) and the rabble (the under class).

This eventually destroys the society because the elite strata itself is drawn from a small selection of the children from the middle and underclass who are identified as having elite qualities and are put into elite schools and other elite conditioning institutions. When you don’t even show these types of children what high culture even is then they don’t have an avenue to express and develop their elite talents and sensibilities, then they never get identified, or perhaps the special tracks and institutions for them don’t even exist by that point

This eventually starves the elite strata of genuinely elite people