Workers from Africa/Asia are lured to the middle east for the promise of a good wage and the possibility of helping loved ones back home. When they get there, they have their passport taken, are given jobs which aren't remotely like those they were offered and are essentially forced to work as slaves in appalling conditions with no hope of ever leaving.
Google "qatar slavery world cup" and do some reading. Just one of many examples of this happening in the modern world, Dubai is another.
So, really what you're asking is "why should I care about slavery?"