because I don't want to write a script (let me know if you write one though) to add functionality that every other control panel I have used/tested (zpanel,ispconfig,cpanel.kloxo,ehcp, etc)as well as plugins for this particular panel already provide. As far as I can tell DA is only one that stores only 1 backup. If I did a script I would have to do it in a manner that allows choices of the backup to restore also and that is probably beyond my coding capabilities.
I think it should be built in, hence posting in a feature request forum, as a backup system with only 1 stored backup is severely limiting, and if admin/reseller configurable the size/space management should be ok.