I can install drop box in under ten minutes. I don't have to manage security patches for all the binaries in the stack. My data is available in network edge locations close to me or the people I share it with. I can turn dollars into more storage very easily. I don't have to configure user permissions and groups in more than one place.
Also, what you described is not "sftp + cvs + vps" ;D
Syncthing makes Dropbox look downright barbarian. Especially if you combine Syncthing with Android and a NAS or home server. iOS is... not really capable of sync outside Apple ecosystem. And this is true even with Dropbox. Not an Android fanboy. Just stating the fact. I take a picture on my Android phone and I don't have to think about it. It's now on my home server, it's encrypted, it's automatically backed up, etc. I have an app that takes a backup of my phone and puts it in a single file. Literally I press a button and my entire phone is backed up via syncthing. I use KeePass. My passwords are in sync at all times, on every device. There is also KDE Connect, which I have yet to try out.
Even before Syncthing, Unison existed since 1995. Which was the true free software version of Dropbox. You never needed a bunch of hacks to get automatic sync working on Linux. Syncthing is a bit easier to configure, IMO.
Can you right-click a large file (in your day-to-day file manager), hit Copy Link, and email the link to someone so they can download it (without having to give them any further credentials)?
Also, what you described is not "sftp + cvs + vps" ;D