Now that we all know what's inside the McDonald's McRib (for better or worse), the question is: Why isn't this notoriously sought-after sandwich offered year-round like the Big Mac? First introduced in 1981, the McRib creates a frenzy whenever it makes one of its semi-rare appearances on the menu. What's responsible for its famed elusiveness? Here, four theories:

1. Pork is pricey and unreliable

In the U.S., pork is generally less plentiful, and thus more expensive, than beef. The fluctuating "long-term nationwide availability" of pork probably means that a year-round McRib "simply isn't feasible," says Matthew Yglesias at ThinkProgress. Even if McDonald's wanted to buy up enough "pig goo" to keep the McRib on the menu, the very act of increasing the demand "would raise the price of goo to the point where it's not economical to keep selling the stuff."

2. The McRib is a loss leader

"The excitement of a limited-time-only product gets people in the door," says Willy Staley at The Awl. People are, "on average, impulsive and easy to fool." Once McDonald's has lured them in with the "low-margin" McRib, customers are likely to "buy the big drinks and fries with the Monopoly pieces" — which is where McDonald's makes its real money.

3. Scarcity feeds the hype

The McRib's cult following has a lot to do with the fact that you can't always get the strangely ribless sandwich, says Nicole Carter at Inc. "Scarcity works." McDonald's has created a self-sustaining buzz machine in which fans post online about "'confirmed' and 'possible' sightings of the McRib across the United States." If the McRib were as ubiquitous as the Big Mac, there'd be nothing to exult over.

4. Maybe it's not as popular as people think

"The last, and most obvious, explanation is the official version of the story," says Staley. Maybe people aren't gobbling up the McRib as ardently as we think. Its first appearance from 1981-1985 lasted only four years. It managed a second stint from 1994-2005, before shifting to its current, infrequent rotation. "Like Star Trek [and] Arrested Development," the McRib lacks mass appeal, "even though a small and vocal minority [love] it dearly."