Why don't use "sparse" option when copying/extracting image files

As I understand, opennebula copy image files (loop devices) when creating images and deploying VMs.

The scrip to copy image file seems to be
/var/lib/one/remotes/datastore/fs/…/downloader.sh

It uses “cat”, “tar” commands to make image files in datastores.
Then why don’t use “sparse” option?
I believe with this, we can save much more spaces.
(I know with sparse files, it will be more complicated to know the “true” free storage space, but still I want to save resources.)