The McRib is back. Here's why McDonald's doesn't sell it year-round

New York (CNN Business) McDonald's McRib is back again.

The fast food company announced Thursday that the barbecue sandwich will be available in over 10,000 restaurants as soon as Monday. But, McDonald's said, the menu item will only be around for a limited time.

That's by design. Seasonal items are an important marketing tool for the food industry, according to Alexander Chernev, a professor of marketing at Northwestern University's Kellogg School of Management.

Limited releases almost give consumers a Pavlovian response. For example, when the weather turns colder, Starbucks customers habitually get excited about Pumpkin Spice Lattes. In November, customers come in to check out the new holiday cups.

"When you have these exclusive products, which exist for a short period of time, it gives people a reason to come to the store," Chernev explained.

It's not just Starbucks (SBUX)and McDonald's (MCD) that come out with seasonal specials: Dunkin (DNKN)' announced a whole slew of pumpkin-flavored treats in August. As the holiday season gets into full swing, we'll be sure to see Coca-Cola's (KO) Christmas trucks, turkey sandwiches from Subway and more. In the spring, it'll be Girl Scout cookie time.

For fast food chains in particular, which rely on familiarity, holilday items can offer consumers some variety.

"You need consistency because that's the brand mantra," said Chernev. "But no matter how much you like something, consuming something different ... increases the enjoyment of what you consumed before."

Chernev says it's a neat marketing ploy: Although a specialty item may be exciting on its own, it can also remind consumers how much they like the basics.

Seasonal offerings can also give brands a chance to test a new product. When Starbucks announced the return of the Pumpkin Spice Latte two years ago, it also unveiled the Teavana Pumpkin Spice Chai Tea Latte.

And Chernev pointed out that seasonal menu items mean brands have something new to talk about every quarter.

Starbucks has said that's part of the rationale behind its seasonal drinks

"We strive to provide our customers with unique, seasonal offerings to celebrate each season, and customer response has been extremely positive to that," a company spokesman said two years ago.

There are some basic supply-and-demand economics behind limited-time releases too: Scarcity can build hype.

"It's a way to create excitement for the menu," said R.J. Hottovy, a consumer strategist for Morningstar.

Items that might be popular for a few months probably wouldn't generate enough year-round demand.

When the McRib debuted in 1981, it was a dud. McDonald's pulled it from its menu four years later. Though it never achieved nationwide success, there were parts of the country where the McRib generated a solid enough fan base to bring it back every now and then.

Hottovy explained that sales typically rise for a short time when companies unveil seasonal items. But after a few weeks, that demand drops off after the core fans of the limited time product are satisfied.

So enjoy your McRib sandwiches while they last. And let's be honest, you probably wouldn't want one in April.