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Some of them actually did graduate from "ice cream academy". Local Ice Cream parlor has reputation to maintain. Sometimes it is even directly operated by ice cream company.
McDonalds just runs automated machine somewhere in corner. They have no reputation to maintain, it is just borrowed franchise.
Nobody in Russia cares if some local private/municipal theater plays DVD rip of Barbie...
There is a chain of custody, paper trail, spare parts certification, logging... For example if there is a heat ex-changer that sometimes does not work, it may cause a lawsuit. McDonald (and insurance companies) wants to be able to sue ice cream machine manufacturer.
I also want to be able to replace any "suitable" parts in my car, but sadly government does not allow that! Remember, when everyone lost their shit with Volkswagen "cheating" in their software?
Meat is cooked just before the use, it does not get poisonous very easily. Ice cream is very different. How would you ensure that managers throw away "good enough" batches of ice cream every evening?
But we let worse things slide, so who cares. Enjoy your ice cream! :)