It's been a limitation since AoS, they said.
I never noticed, but then it was just luck as to what combination you got on loot. I looked back through all my old jewelry and sure enough it held true.
I guess it's to limit certain powerful combinations, but it seems most of the complementary skills are available together. Maybe it's just to reduce the amount of math involved.
But yes, I wanted a set of Magery/Music jewelry for my carpenter so I could make both circles and instruments without needing to swap jewels. Neither come up that often so it's not a huge issue.
It was part of the design system of game. All the skills were grouped into 5 distinct categories, which for the most part had the major combat templates of the start of AoS reflected in them. Only artifacts and event items could have multiple skills from one group (hence, the Mark of Travesty).
Skill Groups (columns reflect the following templates - Mage / Bard / Warrior types / Tamer / Thief (and Ninja*) ) (* Added after AoS)
Group 1: Magery / Musicianship / (Swords, Macing, Fencing) / --- /--- / ---
Group 2: Wrestling / Provocation / Tactics / Spirit Speak / Animal Taming / ---
Group 3: Meditation / Discordance / Parrying / Focus / Animal Lore / Stealth
Group 4: (Evaluate Intelligence, Mysticism*) / --- / (Bushido*, Necromancy, Anatomy) / Veterinary / Stealing
Group 5: Resist Spells / Peacemaking / (Healing, Chivalry, Archery, Throwing* ) / --- / Ninjitsu*
Interestingly enough, there was a typo in the system originally, and the skills in Group One (that Devs originally referred to as Group Five, as if multiple skill groups end up on a naturally spawning loot item, this group was always last in priority of display), only spawned at 1/100 of the rate of the other skill groups. As a result, for the first year or so of AoS, Magery, Music or melee weapon jewelry was EXTREMELY rare.
