Okay, that's not why I intended to make a post just now, but I have to address that: *slow clap* NICE!
As for this thread's topic, yeah, I'd like to see them riff more blockbusters, too. And I think they will in the next few months as the big movies from this year start coming out of DVD. Sure, there are lots of existing blockbusters they could do, but I think I know the real issue here.
Think of how many times they've had to watch the Twilight and Transformers movies over the last couple years, AND High School Musical, AND The Last Airbender. Countless times I'm sure. So I imagine they each said "Okay, I've had all of this that I can stand. I see two options. A) it's time for the ol' head-in-the-oven, or B) we take a break and riff different movies for awhile."
It was a hollow threat, since everyone knows the oven at Rifftrax is electric for this very reason-- they made the switch after losing half their writing staff while working on The Room-- but the point had been made, they were in need of a break.