While I don't doubt that happens, the article shows complexes surrounded by walls and numerous guard towers. I think it is safe to assume that most of the people inside these facilities are not there voluntarily.
Following the attempts to dismantle the scam ring in Myanmar, many rings moved their base of operation to Cambodia and continued from there. That's the reason I described the scenario in Cambodia, as it's more recent, though I also recall the similar news and discussions about the scam ring in Myanmar as well.
GP commented about Cambodia, but the article is about Myanmar.
Maybe that can explain the difference. (If slavery is more prevalent in Myanmar)