Here's the problem. I could understand that if a lot of these folks were visiting from a cruise stop but the vast majority were there specifically for a land vacation. It's unlikely they were on scopolamine for motion sickness. Not impossible, just unlikely that many people were.
No, I think it is more likely these folks displayed something these perpetrators found valuable (inadvertently or not) making them a target for theft, robbery, etc. And think about it... almost all of the victims (who didn't die) had to shell out exorbitant amounts of cash just to LEAVE Mexico.
Seems the bartenders target the victims, drugs them, and the hospital fleeces them.