The Shamrock Shake is back. Here’s why you can’t get it year-round

The Shamrock Shake is back again.

To honor the 50th anniversary of the drink, McDonald’s is making it available for purchase throughout the United States starting Wednesday. It’s been three years since the shake was last sold nationally. In addition to the traditional green vanilla shake, McDonald’s is selling a McFlurry version made with Oreo cookies. Both drinks will be sold for a limited time.

Temporary offerings like the Shamrock Shake help McDonald’s create buzz and bring in nostalgic customers.

McDonald’s first started selling the drink in 1970. Over the years, the burger chain has brought back the original as well as variations of the shake, like a “Shamrock Sundae” in 1980 and a chocolate version in 2017. It first started selling the item nationally in 2012.

For fast food chains, which are constantly competing for customers’ dollars and attention, specialty offerings are a way to try to cut through the noise and give people a reason to visit stores.

Plus, seasonal offerings help get customers in the habit of coming in at a certain time of year. Ideally for the company, people will associate fall with Starbucks’ Pumpkin Spice Lattes, or early spring with a Shamrock Shake.

Chains are unlikely to add these types of items to their regular menus because they’re such an important marketing tool.

Plus, while people get excited for Pumpkin Spice or Shamrock Shake season, they may not actually want the indulgent items all year round.