A century ago so few people graduated from high school, or even elementary school, that what was measured was how much schooling they had, not how much schooling they did not have.
Today we have the luxury of conceiving of "dropping out" as a problem because most people get so much more schooling - and better schooling - than they used to. This is a huge improvement that we take for granted.
The positive way to see the same facts is that we have a very high high school graduation rate today, compared to the past. And it is getting higher.