I wonder if high levels of systemic melanin inhibits adrenochrome oxidation to melanin.
I wonder if in certain races adrenochrome has a prolonged existence when instigated through fight or flight due to this inhibition.
Certainly if true, that would make them more high demand.
As for the question of "why not synthetic adrenochrome?"
I suspect it's because to stabilize adrenochrome it needs to be polymerized with a stabilizing salt (bismuth is the preferred in the aforementioned 3M patent). This no doubt effects purity.