Air defence
If CVF / air defence has been an RN priority for the last decade, they've got a bloody funny way of showing it by retiring the SHAR !
In reality, maintenance or even upgrading / making new jets would cost peanuts by military standards -though the fact is internal politics at BAe mean Harrier is a dirty word, it embarrasses the Whippet botherers.
If commonality with the Joint Force Harrier 2 was a big deal, a few Harrier 2+ with AMRAAM ( radar not as good as SHAR, but a bigger engine & other goodies) would have fitted the bill nicely.