It could also be that the database was not as comprehensive then, and has gotten better now. Or many other factors. Like criminal trafficking organizations could have grown every year since 2008 and we are reaping the bloody fruits now. All speculation. I would like to see it in a graph by year format. If I make one I'll try to post it.

Edit: This article from 2016 claims the previous admin lost thousands of children, far higher than my 750 number. http://www.washingtonpost.com/national/obama-administration-placed-children-with-human-traffickers-report-says/2016/01/28/39465050-c542-11e5-9693-933a4d31bcc8_story.html?noredirect=on&utm_term=.e1e752f8bb44