In almost every single case, those using these drugs are trying to escape the physical and/or emotional pain. They didn't wake up one day and say "I want to have fun, I'm going to do heroin"
Almost every fentanyl user I've talked to in harm reduction work started out on prescribed painkillers. Whether they got the taste and moved up quick, or just couldn't get their fix and couldn't deal with the horrible weeks of withdrawal and found a place to get it, they didn't just up and start shooting fentanyl one day.
1: https://drugabusestatistics.org/prescription-drug-abuse-stat...