IIRC when Fisher proposed building the original "Dreadnaught" one of the objections was that it would mean we'd have to build new drydocks to take her and her successors.
He pointed out that wars are not fought by dry-docks. (and Tirpitz said the same thing about rebuilding the Kiel Canal).
How much would it cost to build another one capable of handling the Astutes?? There's clearly a desperate need.