Current pharmaceuticals are usually a (life)long prescription. It’s not like antibiotics, where you get a dose for a few days or weeks and you’re done. Antidepressants have to be taken for years. Every day. That means revenue every day. It’s a treatment, not a cure.
MDMA on the other hand is a (potential) cure. You take it a few times under supervision and that’s it.
Problem is, this takes away customers from the former group. And that means, far less revenue from “traditional” psychopharmacology products. MDMA cannibalizes other drugs.