^Because there is a thing called tolerance. Also, taking opiate every day of your life will certainly leave you depressed. I had access to very good heroin for cheap, as well as piles of pills, scripted. Was I happy? No.. it became a miserable existence.
Suboxone is for people who are TIRED of chasing that high.. dealing with tolerance.. and want their normal life back. It helps keep their receptors happy while they work on the EXTERNAL problems in their life, that may have led them to chronic drug addiction in the first place. Opiates will have you by the balls in no time. And it seems like you are just in denial and think because you have a script for oxy, then life will just be dandy for ever and ever.