Tremors/WMG

Burt Gummer is immortal.
During the first film, Burt states that he chose to live in Perfection because it was geographically isolated and specifically that he chose where his house is for the same reason. Cut to the fourth film and we see an apparent ancestor of Burt's named Hiram, who says that he's chosen a spot on a hill on which to build a house which is heavily implied to be the same spot his "great-grandson" lives on later.

Simply put, Hiram Gummer kept on living, and due to being really old has had his memory fade so that he doesn't remember the Graboids (or Dirt Dragons, whatever), only that there's some terrible danger to be paranoid of. Over the decades he's likely projected that fear onto the Communists and even the U.S. Government, thinking those were the real threats.
 * Supporting fact: Burt is the only character in the whole series to survive being swallowed by a Graboid.

El Blanco is a Mixmaster mutant.
There is no true correlation between albinism and sterility, and the number of Graboids in the world is so tiny that the odds of one having even one of these mutations, never mind two, is bound to be astronomically small. It's far more likely that when El Blanco was just a "dirt dragon" larva, he wandered into one of the secret lab's ventilation ducts and was exposed to Mixmaster, which contaminated his genes with those of some non-Graboid organism (perhaps a white lab rodent?) with a conventional life cycle. When he grew to Graboid size, these genes became incorporated into his new form, altering his color and eliminating his capacity to produce shriekers.

Ass-blasters aren't hermaphroditic, and Messerschmitt is male.
We know that shriekers are able to breed parthenogenetically, because we've seen it happen. It's likely that Graboids are either asexual or self-fertilizing, as every Graboid (except El Blanco) that lives long enough gives "birth" to shriekers, even Graboids which hatched out alone. But it's almost unheard-of for complex multicellular life forms to forego sexual recombination completely -- there's too much evolutionary advantage to be had in creating varied offspring -- so it's plausible that at least one stage of the Graboid life cycle would reproduce sexually.

In the third movie, the ass-blaster that killed Miguel was examined after death, and found to be carrying eggs. These eggs must've been produced very quickly after it metamorphosed from its shrieker form, as the entire film takes place over only a few days; however, this isn't out of line with how rapidly the Graboid species appears to grow at all stages of life (fast metabolism). Presumably, it -- rather, she -- would've flown off to lay them as soon as she'd eaten enough to sustain her for her journey. The other ass-blasters' ravenous attacks may have been spurred on by that same drive to migrate and disperse eggs.

And yet, the one ass-blaster to survive the films, the captive Messerschmitt, opts to return to Perfection upon escaping, rather than flying off to lay eggs after consuming the thieves who stole it in Vegas. No mention is made, in "Blast From The Past", of the risk that it might lay eggs; once identified as Sigmund & Ray's animal, it's referred to as "he" throughout. What's more, all other Graboids or shriekers that appear in the TV series -- even the ones purchased for research -- are derived from wild-caught specimens, not Messerschmitt. Were ass-blasters capable of parthenogenesis, you'd think that Sigmund & Ray would have an ample supply of eggs to sell to interested researchers ... and that we'd see larval dirt-dragon models in Jodie's store, as well as other life stages, since these would've been observed when Messerschmitt's eggs hatched.

Conclusion? Messerschmitt really was rightly referred to as "he", hence had never laid eggs, and had flown all the way to Perfection in hope of finding other ass-blasters -- i.e. fertile females -- still there. His picky eating habits were as much a result of his having sex on his mind, rather than food, as of having been spoiled by Sigmund & Ray. The fact that he's male, and doesn't have to fly long distances to seek a place to lay eggs, may even explain why he fell into a "food coma" in the first place: he didn't have the use for all those excess calories that a female ass-blaster would, so took a nap rather than flew off to find a nesting site. Nancy and Mindy are only alive today because it was him, not one of the females, that spotted their body heat on the rooftop.

Cheer up, Burt. You really did need to blow up your bunker: eating MREs would've only put the male ass-blasters to sleep, whereas the females would've scattered across the state and spread the Graboid menace beyond Perfection Valley, with no granite barriers to confine them.