I completely agree but I would add that a lot of people start out by using folders but it needs a little care and attention to keep it all organized so they end up with a few folders that contain everything.
The beauty of a filesystem is that it is somewhat independent of the applications that use it. So if your photo app index gets borked then you haven't really lost anything too valuable - apart from any meta data that is not stored in the image itself. Put everything in a database and you risk bricking the entire computer as far as the user is concerned. Of course this applies to files and folders as well but these are a little more battle tested.
Way back in the early 1990s Microsoft's Cairo was supposed to be based on an object database which got rid of files and folders. Sine this is a relatively old idea I'd be interested to know why folders have not been replaced yet.
You're assuming the database is tied to each application; that's only one possible approach.
NEPOMUK (currently a KDE project) is an example of a database which is independent of any particular application. It stores RDF metadata about each file (and about other things too, like contacts, events, etc) and provides a common ground for any application that connects to it.
In the end, the filesystem is just a key-value database too...
Yes and no. Google Desktop was a fully contained application; indexing was just an internal mechanism for its own functionality.
NEPOMUK is closer to an actual filesystem, in that it's not user facing; it's a service for other applications, like email clients, media players, etc. This allows them to almost effortlessly¹ share information like user contacts or music metadata.
¹ Apparently, a basic but functional email client can be built on top of the platform in 10 minutes.
The beauty of a filesystem is that it is somewhat independent of the applications that use it. So if your photo app index gets borked then you haven't really lost anything too valuable - apart from any meta data that is not stored in the image itself. Put everything in a database and you risk bricking the entire computer as far as the user is concerned. Of course this applies to files and folders as well but these are a little more battle tested.
Way back in the early 1990s Microsoft's Cairo was supposed to be based on an object database which got rid of files and folders. Sine this is a relatively old idea I'd be interested to know why folders have not been replaced yet.