While some of that might be true, explain to me why an organisation like macdonalds would allow up to 30% of such machinery to be out of working order for years and years in high value areas.

Your analysis posits what, that they’re just blatantly incompetent?

I don’t believe that.

If the economics of a working ice cream machine were that good, it would be a solved problem.

You don’t run an organisation like MacDonalds with a basic inability to maintain infrastructure. Imagine if that was true of fryers? Or microwaves? That almost never happens. It’s clearly not a technical problem.

The only way that you could justify the continued maintenance failure you see is if the benefits of a working machine were negligible at best.

Perhaps what you say might be true in general but in this specific circumstance I think you’re applying an “in general…” kind of logic (like “in general more unit tests are better…”) which doesn’t ring true here, to me.