They only had 12 episodes, each one 30 minutes (apart from the finale) long, which wasn't enough time to develop the huge magnitude of plots going on, such as E with Ashley/Sloan, Turtle and Jamie, Johnny Drama and his network, Andrew Klein going crazy etc.
I think the best example was the plot with the stalker. It started well and could have developed into something good, I mean, Vince having a crazy feck of a guy after him would've been great, or something like that, but instead they went "oh shit, we've 3 episodes left to wrap everything up in an epic fashion, uh ... oh yeah, Turtle is in college now, let's just say these sorority goals stole his underpants as a dare, brilliant, plot done, let's move on"