Some rehab centers are shady operations ran by unscrupulous con artists, but I would guess those are a small minority. Most of the people involved in that industry are well-intentioned. The central, core problem in most cases isn't type of provider or methodology employed. The problem is the nature of addiction itself. Approximately 6% of those who drink alcohol will progress to the point they become addicted to it. I would guess (without knowing the statistics for it) a similar percentage of drug users become addicted to their drug of choice. Of those chronically addicted drunks and druggies, over half will take it all the way and drink or drug themselves to death. Why? Because they make a choice to keep going even knowing where it leads. They're the slaves who have learned to love the massuh, the hookers who love their pimp, the battered wives who stand by their man and will never leave him even though he's using them and killing them.
And no, relapse isn't a normal part of recovery. I contest that assertion every time I encounter it. Relapse means whatever the drunk or addict was doing to stay clean and/or sober wasn't working. Don't do what doesn't work.