> The UK has done the costings and VTOL is cheaper.
Sure, but that decision was made before the full trainwreckage of the F-35 was clear. In hindsight, with what we now know of the cost of the program, perhaps the decision would have swung the other way.
You need a much more expensive training pipeline to get pilots who can do arrestor wire landings and they need to keep practicing it, doing this also results in more accidents which result in the loss of the aircraft.
The VTOL system also allows a country to more easily switch pilots from being based on land to using the carrier.