The drug den is a "roguelike" game mode - that's why every run resets your level to 0 with no perks, temporarily. The point of a roguelike is typically to start off from scratch in a randomly generated dungeon and test how far you can go - start with no items/level, power-up your character through found/looted items and experience obtained from fighting enemies along the way, and hope that RNG is on your side, all the while. c: