I knew you would say that, and that worries me since we know that (even according to BP-verse lore) there was at least two Orions in Sol at the end of the Great War.
And? Let's look at this again.
First of all, after the node collapse, the GTA 1st Fleet slowly collapsed as funding was withdrawn. Which, probably, meant that its ships were initially mothballed or scrapped.
When the UEF emerged as a governing body and started to rebuild a fleet, they chose to move away from the "One big Destroyer supported by numerous cruisers" approach of the GTA towards a fleet model of having numerous sub-Destroyer ships (termed Frigates), where each fleet element had the same or equal firepower as a Destroyer while having smaller crew requirements and higher maneuverability overall. In other words, they built a fleet better suited to the task of policing a single star system as opposed to a multi-system alliance.
When Byrne started arguing for the Solaris class, his main argument was that while the Frigate Navy was very good at policing the solar system, in the event of a shivan incursion into Sol heavily concentrated firepower and distributed command were a necessity. As the UEF economy had recovered enough to absorb the cost of designing, building and maintaining these beasts, he was able to acquire the funding necessary.
Now, could the UEF have reactivated and refurbished the Orion class? Yes, certainly. But it was argued that Orions would have required a massive refitting in order to work within the tactical and strategic framework developed by the UEF Navy, while at the same time sending an unwanted political signal.
As a result, if the Orions hadn't been scrapped already, they certainly would have been after the Solaris class was approved; after all why keep those dinosaurs around when you can get a completely new, made-to-fit design that can slot right into the existing fleet doctrine? A design that is, in all aspects, superior to the Orion?
Now, you're arguing that reactivating these ships would be a good way to bolster the fleet in the face of the GTVA invasion. As previously discussed, doing so (presupposing that there are hulls waiting to be reactivated that is, which ISN'T THE CASE) would divert ressources away from building and repairing fighters, cruisers and frigates that the crews are used to.
In the UEF's estimation, old Orions would require a significant amount of up-gunning, as their point defense is sorely lacking by UEF standards. Their primary firepower comes from obsolete blob turrets, replacing those with mass drivers or missile launchers is prohibitively complicated; it would be like taking an Iowa-class battleship and remodelling it into an aircraft carrier with ICBM capability. So no. It does not make one bit of sense to keep them around, or reactivate them.
Sanctuary, and that one that would have fought with the Lucifer.
As discussed above re: the GTD Washington. Regarding the Sanctuary, pretty much the same caveats apply, plus added concerns regarding her structural integrity and the fact that after 5 decades of being a sleeper ship, it pretty much can't be relied upon in a modern combat environment.
There are also a few other story reasons why it hasn't made an appearance, but those are, for the moment, classified.