Many reasons:

* I am not working at the moment and have some free time (shameless plug: resume at my profile), so I want to bound the amount of time I need to get something useful

* many archiving/backup workloads are WORN (write once read never), that and many streaming workloads (data processing, media streaming) don't really benefit from cache. (Unless your cache is as big as your data, but that's usually not why people use S3)

* for the use cases that cache can help, I think you can just use another layer of caching filesystem. I intend to write one if one doesn't exist already. I wonder if you can use cachefs with fuse filesystems? Let me know your use cases and I will think about it some more.

As far as I know, FS-Cache does not yet work with FUSE, though we (in Gluster) and others have often considered adding such support. You can actually get some caching within FUSE itself, but I think you have to go down to the low level (inode-based) interface to get any control over it.

the go fuse binding that I am using only has low level interface anyway. That said I think the parent meant on disk cache not vfs cache.