The main reason is that the ice cream machines take forever to clean, taking up to four hours to sanitize—and it has to be done every single day. When the machines are in the process of being cleaned, they can’t serve ice cream. And, when the staff is handing out Big Macs left and right, no one has the time to tend to the laborious machine.
In early 2017, McDonald’s announced that they were going to be replacing their soft serve machines with ones that are easier to maintain and wouldn’t take as long to clean. However, actually installing the new equipment in every restaurant is taking a very long time and customers are still complaining.
So for now, you may have to keep your McFlurry cravings to a minimum until all of the new machines are in place. If you really can’t control yourself, an extremely fed up customer kindly created an app that lets you check if the ice cream machine is working at the McDonald’s closest to you.