I've been assuming it was some sort of profit motive as TX has been pumping money into it. It seems like there might actually be science driven though. For tramatic brain injury combined with ptsd ibogaine causes a release of glial cell factors that help neuroplasticity wire around the damage. Its also horribly unsafe from a cardiac perspective so you would need a constant eeg during therapy driving up prices. So probably a little of the original motivation too.

DXM is also the active ingredient in the antidepressant Auvelity (combined with bupropion)

Lot of interesting studies and anecdotes on its efficacy as an antidepressant

Maybe I have a liberal view of ballpark sizes but:

https://en.wikipedia.org/wiki/Ibogaine

"The action of ibogaine at the κ-opioid receptor may indeed contribute significantly to the psychoactive effects attributed to ibogaine ingestion; Salvia divinorum, another plant recognized for its strong hallucinogenic properties contains the chemical salvinorin A, which is a highly selective κ-opioid agonist"