McDonald's is popular, at least this is what I was told in business courses, because people like familiarity and they know when they get a meal at a McDonald's it's going to be mostly the same everywhere. Uber doesn't really enjoy that. They do enjoy that it is a unified app and service no matter where you are, they have that going for them for a certainty, but they do not have control over their drivers to the level at which McDonald's has control over their franchisees. That's down to the fact their drivers are independent contractors, although it likely couldn't work any other way. It might be moot since the service is the same, getting from point A to B, so the part people want stays the same.
I would almost be inclined to see it as Uber being more valuable for their management of driver reputations than the software they provide, really. They set a standard, and hold drivers somewhat accountable to that standard, which is something that a more 'open' solution would make very difficult or impossible to do.