Hi there, Harp Op here.
When we started out building Harp we wanted to provided an unparalleled user experience and not compromise on features. Collaboration was a must, after all software is written by people and teams.
Asking for full access was not something we wanted to do, but something that was necessary to get that feature and make Harp Platform a more compelling.
The Harp Platform is not build on Dropbox, it is build with Dropbox support and we can introduce other methods for syncing files and content. Github support is will underway.