Because the McDonald's ice-cream machines are always broken. Elsewhere. You just went to one of the ones that worked.
Serious Answer, from what I understand on the matter:
There's a proven decade+ long repair racket between Taylor (the company that manufactures the McDonald's ice-cream machines), and the McDonald's Real Estate Corporation. At the heart of the issue, McDonald's franchises are contractually obligated to buy a certain model of Taylor ice-cream machines, sold at 18K apiece up front. These machines go through a routine cycle which involves heat treating the ice cream to a certain temp to pasteurize it, but the cycle fails, and the machine spits out a code on the screen that's absolute gibberish. It doesn't allow for other operations of the machine until the cycle goes through successfully, but it can't be done successfully because it always fails, and the machine provides no actionable information to say why it failed, except maybe the machine was either too full or not full enough so it didn't reach the required mandated temperature to finish the cycle.
The actual fill level or proper temperature is never detailed in the manual. In fact, the manual's response to just about every issue is "Call a technician". A technician from Taylor has to come out, interpret the tea leaves-- I mean, code on the screen, and then fix the machine by inputting a code. The repairman gets paid the big money, leaves, the machine gets broken again, the repairman has to come back again. Job security. The idea is that Taylor intentionally programmed those models of ice cream machine to suck, and McDonald's REC gets a kickback from that because the franchisees have to pay Taylor and Taylor pays the McD's executives-- whether it's via their ownership of Taylor stock, or there's a family relation between execs of both companies, or an executive or three is on both boards of directors, or all of the above. Taylor gets a whole quarter of their profits from repairs, so it's in their best interest to keep the machines breaking. And other fast-food chains that use different Taylor models (Wendy's, etc) don't have this issue.
A startup called Kytch invented a device that could connect to the McDonald's ice cream machine. It could interpret the internal communication going on in the machine and tell the staff in plain language what was wrong with it, allowing them to fix it themselves. Reportedly the Kytch device could actually pre-empt a malfunction through pattern recognition and subsequently spitting out what the ice-cream machine was "thinking" and provide staff with preventative measures. It made things fixable. This prompted higher-ups at McDonalds to issue fake warnings about how using the device would put the employees in danger of "serious human injury" and warning them not to use it. It's a f**king mobile-sized device plugged into an ice cream machine.
Taylor then "reverse engineered" (read: stole the data) from Kytch and made their own bootlegged device which "does the same thing" but they would charge the McD's franchises for software connectivity, so they could still maintain a stream of revenue from "repairs", which somehow works better for them than just selling a better machine that doesn't break as often. Or updating the spaghetti code the machines currently run on. Kytch sued Taylor on the grounds of corporate espionage and misappropriation of trade secrets to the point of hiring their own private investigator firm to buy a Kytch device for study. Taylor denied doing that and stated they had no intention to emulate Kytch, then during the discovery phase of the lawsuit, 800 pages of internal emails and presentations came up detailing that the Taylor company actually did mention Kytch repeatedly and specifically how Taylor wanted to emulate specific Kytch features in their own competing product and that McDonald's REC took it upon themselves to stop their franchises from using Kytch devices.
So TLDR; corporations gonna corporate, there was a huge scam, both Taylor and McDonald's REC are a bunch of crooks. Right to Repair for life.
Alternate scenario: This is all part of Darkseid's plan to take out the Justice League before his armada arrives on Earth.
(But no yeah, corporate mismanagement is pretty much all the DCEU is.)
