My first thought was museum pieces, like BattleStar Gallatica was in its show (or about to be). When your planet explodes, you kinda have to take whatever relics you still have around.
So that's whatever outer system junk yard, military collector and used-WarBird dealership the surviving Romulans still had. The survivors wouldn't have much choice in what was left.
I think its a commentary as well as how much the Romulan Star Empire has regressed.
The Romulans could have upgraded these old ships with Borg tech to make them a thousand times more deadly. I think the fleet these new Romulan Imperialists will be using will be pretty fearsome, we know they have the tech to build deadly warships like the scimitar, having old and new upgraded ships will make for an interesting fleet.