I obviously have no way of knowing but I would imagine a combination of: To keep the course "vocational", and relatively straightforward e.g. Working through CLRS wouldn't exactly be a walk in the park.
There is also a - annoying - confusion between programming and computer science, which is probably unavoidable but still gives the wrong idea as to what computer science actually is (Or isn't)
But maybe a required reading? People are taking it as a survey course, an introduction, so it would be nice to give a little teaser or something of stuff that is to come later on.
That's another good point; someone barely learning to program is not at the point where they can understand or see the value in design patterns; at best you're going to create a situation where they blindly create design pattern code without understanding why they're doing it.
There is also a - annoying - confusion between programming and computer science, which is probably unavoidable but still gives the wrong idea as to what computer science actually is (Or isn't)