JT and CT didn't (and still don't) fit nicely into NATO Rank structures.
It was far easier to get rid of JTs and replace them with much cheaper SAC(T)s. JTs remaining in the RAF were effectively dumped from promotion boards as they didn't fit onto SAC(T) parameters (I believe JTs knew too much about their trade!)
CTs are also under fire and have been removed from all but aircraft trades. No more MT, GEF or GRF(CIS Eng) CTs.
Seemingly, the RAF can't figure out how to remove CTs from their lists.....should they promote them all to Flt Sgts? (thereby effectively demoting current Flt Sgts) or make them all redundant (too costly nowadays) or should they promote Sgts to cover those gaps that CTs currently fill? (Making some new form of "Senior Sgt"?)
Existing CTs are given the same status (in NATO) as Flt Sgts - and the same pension rights too.