I think some people have a genetic propensity to get addicted. Plus, maybe you weren’t on the drugs long enough, although some people seem to get addicted very fast.
The belief now is that these drugs create more pain. The medication does something to the nervous system, so the person feels more pain and needs more medication to try to dull the pain. Years ago they used to say that people built a tolerance, that is slightly different. Some addicts say that to feel normal they need the drugs once they are addicted.
Withdrawal sucks, so once you are physically addicted you try to avoid withdrawal.
I have been given Fentanyl (amazing drug) Tramadol, codeine, and morphine (I am allergic to morphine) and I never got addicted either, never felt any withdrawal, but I never took any of them vey long. Half the time when I am prescribed Opioids I don’t fill the prescription.
I took Xanax (anti-anxiety bensodiazepine) for 6 weeks and it was amazing at reducing the acute anxiety I was going through, and I can understand how people get addicted. I stopped on purpose, because I knew it was a very addictive drug. I felt better taking it, and I did keep some with me and take it once in a while for a few more months. I probably would have benefitted taking it a few weeks longer than six weeks in one way, but maybe have become more addicted and harder to stop. Who knows. I was on a very low dose, and when I began to lower my dose I did have increased anxiety again. Popping another pill would have felt much better, except for my fear of addiction.