Probably the traits. Arcane is more expensive robust and healthy much cheaper

the jewelry aint that expensive anymore, due to it been ingame for a long time, plus many have better options by now

Willpower was and still is the best three-piece set in game for Magicka users, since it first became available in the Imperial City DLC. However, there are a lot more set item choices since updates in One Tamriel and Housing (updates 12 and 13), and most end game setups use other sets these days. In addition, you were initially only able to get this set by doing a lot of farming in Imperial City for specific types of trophy fragments, but in Update 12 it switched to any IC trophy type was useable to open any trophy vault - AND you could get Willpower items from doing random dungeon dailies. This increased the supply quite a lot. The combination of reduced demand and increased supply has dropped the prices for the desired Arcane Willpower items from over 60k to around 10k on average, and healthy/robust trait items are near worthless.

You got your hands on some outdated info. With how easy it is to get purple jewelry for other sets + with how much easier it is to get willpower, has caused the price to drop significantly. You use to be able to sell agility and willpower rings in the correct trait for around 100k.

Now if you do enough searching you can get them for 10k-30k.