Provisioning is unique, the only craft skill hidden behind a paywall.
You have to pay NPC's a LOT of gold for Imperial Stock and other items of that tier level, only way to get them is to pay an NPC.
Imagine if Trait Stones came ONLY from paying an NPC 2k each?
no, why would you think that? You can find VR5 level mats in the highest level of any area and in Coldharbour. But you can never find Pinguis, Imperial Stock, Imperial Flour, or the drink equivalents. ESO in its ultimate "wisdom" decided that those should be vendor only, for 61 gold each IIRC