George Washington’s speeches were at a 16th grade comprehension level. Lincoln was at a 14th grade. JFK spoke in 13th grade level prose. Then when Clinton was president, his speeches had dropped to 8th grade level. Why did presidential speech become simpler despite mass increase in public education?

In 1960, only about 40% of American adults over age 25 had completed high school. By 1993, that number surged to over 80%. 

In 1960, only 10% of adults held a four-year college degree. By Clinton's presidency, that number more than doubled to 22%.

Yet JFK spoke at a college educated level, and Clinton dropped DOWN to middle school level.

Why?

Also, when Washington was president, did he speak complex 16th grade language only because he knew the voting pool was wealthy educated property owners? But that won’t explain the decline in speech comprehension grade levels in the 20th century?