Couldn’t say for sure but WebDAV probably would be clunky if fronted by a distributed database. The beauty of S3 is you add more servers, add more disks, and bam you’ve got more S3. That happens most easily when the metadata system sitting in the front can expand easily. I don’t know how easy that would be to plumb up with WebDAV. Whether or not one was better here, S3 ultimately won because it’s a primitive API that was essentially impossible to fuck up.