This is a great question. I once heard a talk by the Global Marketing Director of Ironman who discussed their branding philosophies. read more
Presumedly it is a win-win. In this case McDonalds is likely paying a royalty for use of the Oreo brand to drive milkshake sales, a seasonal category for McD. Of course Oreos (or some bulk form) are also sold as an ingredient for the shakes so there is the benefit of some commercial, wholesale revenue as a manufacturer of the product. read more
Occasionally they may do a promotional flavour (often at the cost of vanilla, depending on the restaurant capacity) e.g. Shamrock Shake or some variation on a chocolate ber, such as Mars or Rolo in the UK. read more
I work at a McDonald's and like others have mentioned, it depends on few factors of why the shake machine is down. 1. Laziness, as someone pointed it out. People are straight out lazy when it comes to a minimum wage job. So of course minimum wage means minimum work. 2. The cleaning process. read more