It's just not true.
Higher income families can afford to take more time off, especially salaried workers, and are often two-parent households. This gives those parents time that hourly-based workers, poor, or single-parent households literally can not afford to spare.
They don't love or "value" their children's education any less, but they are in a situation where being as involved as those more fortunate than them is so much more difficult.
Malcolm Gladwell has written about this - https://www.amazon.com/Outliers-Kimberly-McCreight/dp/006235...