As far as I could tell, the four frost sets never had recipes for head, shoulders or legs. You had to get them as loot in Naxx 60. Please correct me if I'm wrong in that, as I never ran Naxx 60 at the time. Then when they revisited the frost sets in Wrath, they only ever added a few level 80 pieces. I guess they weren't thinking about transmog at the time and figured their use would be too short lived for the full sets to be worth all the work.
Plus maybe they didn't want players getting *too* much frost resistance.
Out of interest, I just compiled an enormous list of crafting recipes that were removed in Cata and sent them to Noah, who was interested in them, and they've apparently been passed on to the itemization team as well. Whether many of them get added back in or not, I'm not sure, but at least they have the list
I also added the level 60 frost gear recipes to the list, since the gear looks so awesome, and pointed out that they'd have to change the mats for them to be useable. We can always hope they get added back somewhere in MoP
I'm not sure where though, as it's level 60 gear and no level 60 areas require frost resistance, or are even cold-themed, so they'd always be more of a nostalgia item.