All those Hornets in storage aren't much help at short-notice if they are not equipped with the same kit as the existing fleet.
The new, networked ADF requires all the toys to have the same bluetooth gizmos so they can talk to each other, the way the Tiger will be able to talk to the Abrams, for example.
And if they have other kit, which is likely, then the drivers have to be trained.
A bit different to the case of having a few "readies" in the hangar, needing only the bungs removed and a quick pull-through.