Hmm, because it's politically impossible?
Labour picked the F-35B in the first place and got a lot of political capital in the Tories changing to the F-35C and then having to change back again.
The Tories lost enough face flip-flopping once, they can't afford to do so again.
What political capital??? voters couldn't give a flying picket what they buy.
I honestly believe it's just down to sheer incompetence, I doubt 2% of politicians could tell you the difference between the A, B and C versions let alone decide which one is required if at all.
The people that make the decisions haven't got a clue, politicians, MoD, whoever. They've got a bee in their bonnet about 'stealth' and it's something we can't afford, but to compound the issue, they decide to buy the version that is less capable and hamstrings the rest of the show.