McDonald's is trying to run an industrial volume process with ingredients subject to contamination and spoilage... using minimum wage young workers with varying levels of attention/dedication to details.
It's a difficult set of constraints that includes a non-negligible amount of blaming the machine for willful lapses in procedure.
McDonald's appears to sell a lot more soft serve (by volume) than any other fast food chain. People go there specifically for McFlurries and others, and then leave disappointed when the machine is not working. Few, if any, go to Burger King or Arby's only for a soft serve product.
So, the issue appears more visible. But that's not evidence that McDonald's machines are less reliable. It could simply be they're the most used.
[1] https://corporate.mcdonalds.com/content/dam/sites/corp/nfl/p...
Point is, they can't even get "no pickles" right.
For reference, here's a first person report from one of the previous times this was brought up: https://news.ycombinator.com/item?id=26938854
Burger King appears to also use Taylor equipment, although not the combo 2-in-1, do-it-all model that McDonald's does.
Wendy's uses a custom machine built by Kappus for their Frosties. [0] [1]
[0] History https://www.wendys.com/blog/history-of-frosty
[1] How It's Made https://m.youtube.com/watch?v=oorX3mHgHQs&t=95s
Also, they're a subsidiary of Berkshire Hathaway since 1998.
The REAL Reason McDonalds Ice Cream Machines Are Always Broken by Johnny Harris
You're getting at the heart of it. McDonalds used to use very simple Taylor machines that were very reliable. The only problem was they had to be taken apart, cleaned, and sanitized at the end of every day. That required an extra employee at closing for about an hour, and another employee the next morning to put the machine back together. This wasn't difficult, but it wasn't totally obvious either so it did require an employee who had been trained on how to do it.
McDonald's wanted to save the training and the $10-$20 of labor, and a few dollars of product waste that this was costing them every day, so they asked Taylor to develop a machine that didn't have to be taken apart and sanitized every day. Taylor did that, and the machine got a lot more complicated. It heats itself up to a temperature that will kill bacteria, then cools back down. If there is a power glitch or fault or for any reason that cycle is interrupted, the machine locks out and has to be "repaired."
Also, as part of the daily cleaning and re-assembly of the old machines, all the O-rings and seals would be inspected and lubricated and replaced if they were cut, worn out, etc. Now that doesn't happen so you get more failures of seals, leaks, etc. which can also shut the machine down.