Tldr: That machine is a pain in the ass to clean. 
The newer ones self clean and while it is over engineered and prone to breaking down, the real reason is the employees dont want to use it or care if you get ice cream.

https://www.allrecipes.com/article/the-real-reason-mcdonalds-ice-cream-machines-are-always-broken/ 

 Drain the swamp! Give us our ice cream