Why Can't Acronis Edit The Full Backup .tib file

I wonder why Acronis cannot back up my .tib, full backup file by looking at what files have changed and replace those files within the original .tibfull backup file with the newer ones. There would be no incremental or differential files to play with, just the new "updated" .tib full back up file. This would be quick because you don't have to create a new full backup file. And you would not be using so much disk space for the full backup file plus all the incremental or differencial files. This seems a far easier solution. What am I missing?