The primary reasons:
- Constant nagging in the user interface to upgrade to Dropbox Pro or Dropbox Business. Don't want it, don't need it.
- Accumulation of a lot of UI clutter over the years. When you used to log in, you just your files. Now you get suggestions, unread comments, or whatever.
- Dropping support for file systems outside ext4. One of my machines uses Linux on ZFS, now I need to LD_PRELOAD shims to make Dropbox work. No, I am not switching back to ext4 for you, Dropbox.
- The camel that broke the straw's back: raising the prices from 10 to 12 Euro per month. It is not like we can't afford it. But storage and bandwidth gets cheaper, but Dropbox gets more expensive. We do not need the new features: why would I need 2TB if I am only using 200-300GB of space? And no, I don't want Smart Sync, which puts itself in ring-0 through a kernel module.
If Dropbox had just stuck to its nice, clean, and simple interface, focusing on syncing across machines with various OSes or file systems, we would still be happy, paying users. They wouldn't have to add anything (though the File Requests feature was nice). Just don't bother me with nonsense and let me do my work and share with family + friends.