Because young people are dumb as fuck too. It's the same reason racism is bad - the distinction between the two groups is meaningless.
For instance, you're incredibly naive if you think congresspeople believe all the shit they say. They're elected representatives saying things their constituents want said even if they disagree with them.
I work with a climate lobby and one of the Republicans I was talking to drives an electric car and powers his house with solar. His official position is "climate change might be caused by people, but the jury is out." He fuckin knows, he just can't say it.