Title.
There is no reason for this to exist aside from forcing scarcity and punishing people who did activities on their main that were under their tier or over-collecting materials when they were in that tier for fear of bad RNG.
To use myself as an example, I had assumed early on that since all major currencies, tokens, stronghold, skill, sailing, and rapport items were shared across your roster that this would include content currencies. Not really a stretch right? Everything else is, including within the same currency tab. However, as I imagine the vast majority of players have sadly discovered this is not the case. As such I am sitting on nearly 100k Harmony shards and 30k life shards I cannot make use of in any way, I have a handful of honing materials that are bound, but that was me over collecting to cover for my bad luck, but only number into the low hundreds.
You have the same issue with honing and upgrade materials, bound potions, utility items, entry tickets, gem powders, etc. It is completely unacceptable that these are not roster bound. Especially when a good number of these things are NOT character bound on the Korean servers to my understanding.