Because we are social creatures and there are still limited resources. Older generations have outsized influence on the tribe based on their experience which ca

Because we are social creatures and there are still limited resources. Older generations have outsized influence on the tribe based on their experience which can drag the rest down. For a contemporary example, consider the real estate bubble. When the bubble burst and everyone realized how badly the banks had screwed up, what happened? Well, everyone who owned a home worried about losing its value. The banks took some stock off the market to hide it, and all the leadership up to the president vowed to do everything possible to "maintain real estate values", even though the "value" was predicated on sub-prime mortgages that people couldn't actually afford. In this way, the older generation whose experience is tied to a particular environment exerts its influence in a way that damages the younger population. Being young and inexperienced means being adaptable but naive and inefficient, being old and wise means knowing how things work and a vested interest in keeping them that way.