I've no idea what the rationale is, or indeed if there is any. I
remember when I installed the first Fedora version that allowed you to
postpone package selection (F7?) being completely bummed out that the
GUI tool couldn't automatically look for stuff on the install DVD.
Baldly telling the user he can do something now or later, without
explaining that 'later' is going to mean either downloading stuff he
already has, or Googling to find out how to hand-edit his yum
configuration, is another example of where Anaconda needs some attention
IMHO.

poc