The intention is to have the database update when the close() is done, not on every write().
It is pretty obvious that the desired functionality could be done by fuse, where a get() is done on open and a put() is done on close if write was ever called.
I think the modern day applications that only write a part of a file are nearly non-existent (and in fact partial update where another program can see your unfinished writing, is usually a bug, not a feature). So there is no need for any api other than put().
There is a nice subset that only reads part of a file (and that part almost always includes the start of the file) however. So I can see this as being an argument for being able to access blocks of data from the remote.