From what I understand (could be wrong): McDonalds forces their franchises to buy these Taylor ice cream machines, and despite the high cost and frequency oof repairs, McDonalds franchisees continue to own and operate McDonalds meaning that despite the troubles, it is still worth it. If the ice cream machine caused a big of an issue, McDonalds would see less franchisees, and discern from their research that the machine was an issue, and change brands.

Again, it starts with the customer. If people really are that pissed off McDonalds ice cream machines are seemingly always broken, then they should stop going to McDonalds, and then the feedback loop will start from there. It's not like there isn't ample other options (Wendys, Burger King, etc). That tells me that this "problem" is really overblown, and while McDonalds customers really would prefer to have the option to reliably order ice cream, it does not deter them significantly enough from consuming McDonalds, and doing something like simply purchasing their ice cream from a different location. If McDonalds wants to recoup that income, then they will, again, prioritize that initiative, and work on improving the ice cream machine, but again, that juice does not seem worth the squeeze.