Why Do So Many Sequels Suck?

(We are treated to the "Sequel Month (the sequel)" title, before cutting to the NC, who looks rather listless)

NC: Hello, I'm the Nostalgia Critic; I remember it so you don't have to. Well, as Sequel Month is winding down to a close, we realize there are some good sequels out there, but there's a lot more bad ones! (beat) Why is that?