LibreOffice being FOSS probably means developers are mostly using it together with other FOSS. This brings some benefits, like a journaled filesystem, that sort of make the autosave useless. That recovery process that failed for you? It wouldn't have on something like btrfs or ext4 and, consequently, you wouldn't have been in a position where you're typing up this post.
Having said that, on bs OSes like windows autosave probably should be the default.