Because for neither China nor the USSR was that the main contributor to their national problems. Further, the education system of both are definitely implementations of "let's spend the most money on the smartest people".

In a discussion about the collapse of societies, it doesn't apply. In a discussion about education reform, it does not apply. It is also not an example of the original commentors statement that conquerors have used social spending to collapse their targets.

I would further point out in both the case of the USSR and China's purge of the intelligentsia; it was FAR more about consolidating power in a dictator and far less about trying to set good national policy. In Mao's case in particular, he was frankly just a bit insane.

There’s a selection bias in that the USSR and China both actually turned into barely functioning societies afterwards, often because they implemented their ideals in inconsistent or hypocritical ways. If you take the same ideology and actually apply it consistently you’re the Khmer Rouge.