It remains perfectly possible to fit EMALS (and EAR) to both QE and PoW. They are designed with sufficient space and margins to receive those systems. What the contract does not (and never did) include was the actual detailed design to system level (ie the actual structural seatings, cutting plans, weld procedures, cabling and power management system software) and subsequent supply of the hardware.
For a variety of reasons (some credible, some less so) the "cost of modification" (which may or may not include other elements) for one ship was "estimated" thiis time last year at £1.9Bn which exceeded what MoD was prepared to pay.
Hence the "reversion" to STOVL.