Obviously there are going to be more total enslaved people now, it scales with the population. The problem with looking at it that way is that it doesn’t actually tell you if the situation is improving. All it tells you is that there are way more people now. That’s why you look at a percentage. That will tell you how bad the problem was, how much better its gotten, and how much better it needs to get.

I’m not trying to argue that everything is ok because a smaller percentage of people are enslaved now. A percentage is simply the more useful method of measuring how common slavery is and comparing it to different times.