Dropbox is no longer primary storage option for draw.io. 2 main reasons:

1) They selected unpkg.com as a CDN for distribution of their JavaScript and unpkg suffered a DNS hack. Dropbox clearly did not audit unpkg (though, in fairness, neither did we), but we feel that the JavaScript client is not treatly as a "first-class component" if quality slips of this magnitude occur.

2) Files cannot be shared.