Dilaudid is not effective for my pain, but weaker opioids are. what's the deal?

Hard to say: there are certain enzymes that metabolize opioids into the active ingredient, which ultimately is morphine. There are people who lack, for example, the enzyme that turns Codeine into morphine, and therefore Codeine doesn't work for them. You may have something similar where hydromorphone isn't metabolized into morphine, or isn't transported to the brain properly.