That may have been the reason for mothballing the old ship designs, but why weren't the new ones nuclear powered? That seems to be independent of the missile launcher design.
* Role of the ship: why have an expensive ship that turns into a radioactive reef in a role when one of its missions is to "take a bullet" for a carrier?
Mainly for cost reasons, plus nuclear reactors also take up more space and can't accelerate quite as rapidly compared to modern gas turbines. If the Navy ever decides to build a new cruiser class to replace the old Ticonderogas then it might be worth considering nuclear propulsion, but realistically the budget just isn't there to make it happen. The Navy can barely afford to provide enough qualified crew for their existing few nuclear vessels.
