Because I'm talking about 10 or 15 years ago, when the indoctrination wasn't nearly so pervasive, adamant, and conspicuous. That has only developed in the last 10 years.
It's been developing over at least the past 30 years. During and after the 60s, lots of left-liberal people from the 1960s era and mindset went into education and became teachers, principals, and professors. It has become conspicuous now, but its roots go back quite a long time.