There were some really wild characters back then. Especially on Letterman, but also on Carson. Nowadays, nobody has anything very interesting to say, and everybody's just trying to push their latest project. In the old days, I actually thought they wanted to be there.
Not one of these late night people, Leno included, ever showcased new talent. Carson had new talent on all the time and actively was always looking, when he retired that stopped, Leno was never secure enough to do that.