you're missing a bit of realpolitik here.
Both the -B and -C are failing projects and will probably get cancelled due to the cost overruns and technical issues.
So it makes no difference which we order - it will get cancelled anyway. The only difference is that if we go with the -B, when that gets cancelled we won't have to pay for the catapults....
The ships will then just be mothballed and probably eventually flogged off to India
Might well be true.
Another possibility is that they want to have the F35 no matter what the cost
will be to assure RR & Bae's F35 profitability, best to assure this is by going for the carrier version that can only use the F35 ,no alternatives possible.
That would also explain the sudden U turn.