One reason McDonalds seems so bland and generic is most of the ingredients come out of a factory, so everything is centralized.
To get fresh ingredients you generally need a local supplier, but then scaling that up must be a logistical nightmare.
Because they only use local suppliers, and they haven't figured out how to get everything they need locally anywhere else.
I've also been told it's a case of freshness. If they have to ship all the ingredients from California to Iowa, it's not as fresh as they want it to be. Keeping the supply chain close and using local suppliers for specific ingredients allows them to have a consistent product no matter where you get it.
At the end of the day, as an owner, that's what you want. No matter where the customer goes, they always get same fresh, great tasting product.