Starting Monday (October 7), the McDonald's McRib sandwich will be sold at over 10,000 of their locations, but, obviously, for a limited time only. The McRib has been an on-and-off item on McDonald's menu since 1981. While it's beloved by many, there's a good reason why the barbecue delight remains seasonal. 

Alexander Chernev, a professor of marketing at Northwestern University's Kellogg School of Management, explained to CNN why McDonald's opts for this move. "When you have these exclusive products, which exist for a short period of time, it gives people a reason to come to the store," he said. Chernev compared the phenomenon of the McRib to Starbucks' seasonal items, such as its Pumpkin Spice Latte. As we all probably know, the PSL ignites a craze every year when its reintroduced to the Starbucks menu right before the fall. However, the drink would likely not perform as well or generate as much buzz were it to be available year-round. The companies get to contribute to building the buzz too, keeping them active and present in consumers' lives. 

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Chernev also detailed how offering seasonal items reinforces the love for a chain's staples, while also ensuring that customers do not get bored of the everyday menu. "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."

Essentially, the success of limited-time items can be attributed to supply-and-demand economics. The less there is of something, the more people want to eat it. 

Check out Dunkin' Donuts' elaborate pumpkin-filled Fall collection