Justicar Thawn and Apothecary Changes

I've coming back to the hobby since falling off in 6th edition and I've noticed there's been a few changes to our roster. Justice Thrawn is relegated to a lore blurb and the apothecaries were moved from only being trusted to be escorted by the Paladins to only working with regular terminators, and I was wondering if GW ever gave any explanations for those changes.