A big part of the problem is that Dropbox is a fundamentally different product than what it used to be. Today's Dropbox is not even attempting to be a tool that

A big part of the problem is that Dropbox is a fundamentally different product than what it used to be. Today's Dropbox is not even attempting to be a tool that simply synchronizes directory contents across all of your machines. Instead, it is trying to be a network filesystem with a local cache, with various other features layered on top. It's a lot more complex, built with leakier abstractions. The original Dropbox could be a viable product to disrupt today's Dropbox for many of the same reasons Dropbox originally achieved success.