Here is a nice paper about the science of opioid addiction.
The 5th page down or pg 17 has a nice set of diagrams of what happens if it's TL; DR.
https://archives.drugabuse.gov/pdf/Perspectives/vol1no1/03Perspectives-Neurobio.pdf
"The likely explanation for these observations is that opioids raise levels of cortisol, a hormone that plays a primary role in stress responses; and cortisol, in turn, raises the level of activity in the mesolimbic reward system"
along with "...methadone, buprenorphine, and naltrexone act on the same brain structures and processes as addictive opioids, but with protective or normalizing effects."
I don't know, there are some decent parts but honestly there is a lot of bad info too. There is a lot of research data which points that opioids tend to lower cortisol, so either the paper is worded in a very weird manner and I'm misinterpreting it or it states things which are definitely not "clinical truisms". While buprenorphine and methadone have their place, they can equally be the problem itself, so calling them protective/normalizing can be outright dangerous.
The part about noradrenaline is pretty important though, it's one of the reasons clonidine is such a godsend. The paper makes it seems though that clonidine by itself could substitute opioids and while it seems to play with the endogenous opioid system it doesn't quite cure opioid withdrawal. When we start making assumptions that more or less same factors lead to addiction/dependence in every case it's easy to start looking at things in a skewed manner. I'm pretty sure there are many others too who never took opioids for 'intense pleasure' but to self-medicate another issue, which in turn often gets exacerbated when opioids are removed from the equation. Pain being an obvious one, but there are many other reasons people end up taking opioids. They are a very convenient way of managing stress that results from various life situations, the problem being that you really don't tend to develop natural (endogenous) ways of coping with stress when you are taking them. Therefore depending on the individual, the endocrine system for example might be way more crucial to addiction compared to the mesolimbic, in my opinion at least. The HPA-axis has a diurnal rhythm and curiously cravings and withdrawal symptoms seem to vary simply with the time of day as well, independent of environmental stressors, triggers, cues etc. Not to say the latter don't play a part too.
In the end, it's all about what we actually do with the research data that counts. For me personally, pleasure, reward, motivation, it's almost irrelevant when compared to training the brain to cope with stress, step by step. For someone else it could be equally important to unlearn the reward seeking behavior associated with opioids. Quite a complex matter. For whatever reason I'm not bothered at all if there are opioids within my hands reach when I'm in acute withdrawal, or if someone else is using them in the same room and when I get cravings they tend to be for anything which isn't an opioid as long as it lowers the stress I'm experiencing (or at least I believe it would do so). Resetting withdrawal by taking opioids is a very stressful idea in itself, so I don't need to put conscious effort to avoiding it, unless the mind tricks me into believing I wouldn't be resetting or setting the withdrawal process back significantly.
Many ways to look at it, best keep an open mind I suppose.