Because every “file” in the snapshot is either a file or a hard link to an identical version of that file in another snapshot.) So this can be a problem if you store many snapshots of many files.

I think that you may be thinking of rsnapshot rather than rdiff-backup which has that behavior; both use rsync.

But I’m not sure why you’d be concerned about this behavior.

Are you worried about inode exhaustion on the destination filesystem?