The difference is scale-out metadata in the filesystem. Alluxio uses Raft, i believe, for metadata - that has to fit on a single server.
The truly amazing part for me is combining NVMe SSD + RDMA + supports reading a huge batch of random offsets from a few already opened huge files efficiently. This is how you get your training boxes consuming 20~30GiB/s (and roughly 4 million IOPS).