Basically, Bastok/Sandy/Windy all have items that can be bought from rank 1-10.
Up to about rank 5-6, many of these can also be improved via crafting, with an NQ and HQ upgrade.
After that? Pfft, upgrades peter out. Even the non Rare/Ex pieces seemingly can't be improved- and even in some lower ranks, there's cases where a piece can't be improved.
Why not? Most ranks 5+ have at least one non EX item that begs for an upgrade recipe, like the L30 Paisley scarf.
Adding in the higher-rank CP item recipes would give folks some new (and potentially effective) items to craft, and if some of those items were high enough crafting levels, a good reason to build up a stock of Conquest Points to give yourself more options to skill up on/make useful HQ's.