And APFS doesn't support directory hard links either, so if your drive is APFS formatted, you back up to an image as well!
So we've gone from just files to a special unique image file.
And people get burned by this: if the image file gets corrupted, you lose the entire backup.
And Apple's been layering stuff on top of it.
There are special ACLs and System Integrity Protection things that prevent you from manipulating the backups in any useful way.
So it's just a proprietary backup system with a nice UI now.