Because young people are silly most of the time. They are clueless of their ignorance and how fast and radically their own beliefs will change over time.

Every 10 years, you look at your own self and you realize how little you knew, how silly and naive you were, and it keeps going.

Wisdom is when that cycle stops, either because you settled on a set of beliefs or because you understand that it's all fleeting anyway, either way, nobody should lead before reaching that stage imo.