McDonald's elusive McRib begins its latest comeback tour today, and crowds are sure to gobble up the fabled sweet boneless barbeque pork sandwich in its triumphant return.

Normally, the McRib is only available when individual restaurants decide to make it. Last year, McDonald's rolled it out nationally for a limited time, and it was successful enough to warrant a second go.

So if people love it so much, why doesn't McDonald's offer the McRib at all of its locations, all the time?

The McRib is -- like every other item at McDonald's -- its own brand. And its branding relies, almost completely, on its own scarcity.

Everything McDonald's does with the McRib pushes that image to the fullest. For example, during the 2010 release, McDonald's fired up its Save The McRib campaign, which called on McRib fanatics to go online and sign a petition to keep the McRib on the menu.

The hype the McRib generates doesn't compare to any other menu item McDonald's could ever hope to recreate. From Time to USA Today to the LA Times to HuffPo to the WSJ to Gawker to Entertainment Weekly -- when the McRib comes back, it's everywhere in the media. And when the McRib's in the news, so is the McDonald's brand.

Why don't they just make other, new special items to create a similar amount of ballyhoo?

Well, the McRib's effect can't be easily replicated. The sandwich was first pulled from the menu all the way back in 1985, and it has had decades to build its cult following. New item debuts may get people psyched for their initial launch, but a wholly devoted fanbase like the McRib's would take years to cultivate -- and there's no guarantee of success.

Making the McRib permanent nationally is too much of a risk to take. Remember, the McRib also gets people into the store to buy even more, and the effect is amplified with all the build-up before its big comeback appearances -- something McDonald's can only get with the McRib and a few other select items. Customers are dragged in by their insatiable McRib-loving friends, since they don't want to eat alone.

If the McRib was there permanently, it'd likely become just another menu item. It needs the desperate yearning of its fans, a year or more removed from the sweet sandwich, to be the hit that it is.

In a few weeks, the McRib will disappear once more, never to be seen ever again -- at least that's how McDonald's wants McRib followers to feel the day the sandwich is plucked from the menu.

So, will it be back next November too?

"It's too early to speculate," McDonald's US marketing director Marta Fearon told Time.

The hype for next year has already begun -- or has it?

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