Mainly because Little House on the Prairie was a television show. You know...it was fictional....written by people, acted by actors....not real life.
The reality is that the average kid that graduates today knows more math, reads better, and writes better, than the vast majority of people even 50 years ago, much less a hundred years ago.
At the turn of the century, it was a big deal if a person was literate, and could add and subtract.
You have got to be kidding me....