The answers are not surprising but they are a great reminder of the product design essentials.
Here’s a magic quote from a competitor who tried to beat them in the market:
I ran into the CEO of Dropbox and asked him my burning question: “Why don’t you support multi-folder synchronization?” His answer was classic Dropbox. They built multi-folder support early on and did limited beta testing with it, but they couldn’t get the UI right. It confused people and created too many questions. It was too hard for the average consumer to setup. So it got shelved.