Current State of End-Game Contents - A Blog Post from A Japanese Player

[Melithea]

Yes, the 3 options available in the game (Crafting, Gathering and Battle) are different, but that's beside the point, the point here is randomness and reliance on the RNG, why its used for HQ Crafting and Gathering and why its NOT used for Battle mechanics.

The obvious answer would be the fact that crafting is an extremely simple system with an incredibly low ceiling. Without RNG it would be "push button, receive HQ item". The fact that the systems are different isn't beside the point at all.