Sure, they smile now...
First off, every film they've directed has been nominated for at least one Razzie and nothing else. If Uwe Boll is the Spielberg of crappy movies, then these two are the Coen Brothers: comedic directors who think they have something to say about the movies they're spoofing, but are honestly just applying fart jokes to them. And they've reaped the "rewards" for their hard work: together they personally share three Razzie nominations, and they'll most likely earn more this year as Vampires Suck has emerged as a Razzie frontrunner. They must be so proud.
This is perhaps the saddest truth of all about them, though: time will not help their case. Some crappy films live long enough to see themselves become cult classics; Piranha, for example. And with their chosen genre being the spoof, one could say: well, Airplane!'s managed to become a classic. Here's the thing though: Airplane! has lasted because the comedy is broad and unspecific, or perhaps timeless, as the jokes are funny to every generation. That's the mark of a great spoof film, and its why Scream and even the first Scary Movie (which Seltzer and Friedberg co-wrote), though not on the same level of greatness as Airplane!, will probably stand the test of time: the jokes are not necessarily specific to the time of the film.
Their filmography as directors/writers. Can you spot the differences?
This is not the case with Seltzer/Friedberg productions. Rather than ape the conventions and cliches of the genres they target, they prefer to go for very specific films and often irrelevant pop-culture institutions (Disaster Movie was certainly the most egregious offender in this case, since it had almost nothing to do with disaster movies; the title was really a prophecy). By doing so, the films instantly date themselves. This results in the impossibility of these films to last. Sure, the jokes are often very broad, but its the same general set of jokes in every one of their films; there's nothing distinguishing about them except for the targets. And because the humor is so specific, the "humor" won't last. These already unfunny films will only become more unfunny with the passing of time. And it won't even take much time: go ahead and rewatch Date Movie, their first solo outing from 2006, and see how much of it holds up. And think about Vampires Suck: there's a throwaway gag (in the trailer) about the cast of Jersey Shore, and sure, they're famous now and everyone knows who they are, but what about 10 years from now? 20 years from now? When future generations watch these films, unless they have acute knowledge of the years in which they're filmed, the jokes will be lost on them.
Its mostly for this reason that I feel sorry for these guys: this moment, when their average Metacritic score is 20 (out of 100), is the moment that their films are at their best. That's got to hurt somewhat.