Because while these new grads and less experienced people maybe quite intelligent, in general they are less capable of dealing with or managing anything properly. I am 54 I go back and forth between an IC and director level management at will.

As an IC, all of my designs just simply work without any drama. What happens in this scenario is that as soon as they learn what they needed to learn from me I am usually out. Also there seems to be some concept of drama and running around like a chicken with your head cut off is "fun" and I am a buzz kill in this situation.

As a manager I spend a lot of my time just making sure that everybody is set up for success as nobody seems to be able to advocate for themselves. Their communication is lacking they don't understand their audience or how to delegate. In these roles I am retained as long as I wish.

Smart doesn't equal knowledgeable and smart doesn't equal efficient. It's that simple. These are things best taught through experience.