I blame the 'It's cool to be ignorant' mentality so many people buy into as a way to avoid doing anything that seems to them to be hard or require some actual effort.
But that mentality is promoted by and advantageous to the ruling class.
The ruling class knows that if they keep 'em stupid, the stupid never figure out they're being taken advantage of and kept down.
In other words, the ruling class has a vested interest in degrading the quality of education.