Modern-day slavery?

From a story on CNN: "But how widespread is what many experts call modern-day slavery?"

It's still slavery. Why is any expert prepending the words "modern-day" to a concept that isn't any different now than it was a hundred or a thousand years ago?

If they just mean slavery today, they should call it early 21st century slavery. That way the label will still work in 50 years when the definition of modern day changes.