Within a couple of years, as streaming video in general became popular, we began to release Video on Demand products, which included the jokes merged right into the movie in a convenient package -- first shorts, then feature-length cheesy movies. These proved to be immensely popular, as they not only required zero syncing, but allowed us to do movies that were NOT recently released on DVD, just like the old B-grade and below flicks that fans used to see on MST3K.
Because of the convenience of these products, and the fact that we can deliver them directly to your TV through your Chromecast and other set-top devices, we have shifted our focus more towards Video streaming products, and less on MP3 commentary tracks.
(Additionally, the guys have often spoken about how difficult it is to riff some of these modern-day blockbusters; many of them use fast-cutting editing techniques, are three hours long, and tend to feel the same as all of the blockbusters that came before it, which makes both the writing and enjoying the riffs harder to get through. We blame Michael Bay for starting this trend.)
We'll still be doing commentaries for movies, but for all of the reasons cited above, they may be less frequent. If you have a movie that you think is deserving of the RiffTrax MP3 treatment, submit it at our Movie Requests forum! We check that list all the time, so get your friends to vote yours to the top, and if we do riff your suggestion you might just get something to say thanks.