> Generally private school teachers make way less than public school ones though do.
Private schools have looser licensing requirements and fewer overall positions to fill, so there's a greater supply of labor competing for a lower demand. That already would lead to lower pay in itself.
They are also able to offer benefits that private schools typically cannot (such as a reduced responsibility for administrative work). Teachers who come from industry or higher education are oftentimes willing to trade a lower salary for the additional flexibility (which they can oftentimes use to pursue other adjacent work in their field.
That's why private school teachers are more likely than public schools to have teachers who old PhDs, despite the pay being higher at private schools, and despite the licensing requirements being less strict for private schools.
Their union won’t let you pay a new hire more than a less competitive teacher with more seniority. Therefore almost nobody with the capacity to work at a FAANG will choose to become a high school CS or Math teacher earning poverty wages.
Texas doesn't have a teachers union and they still don't pay them all that well. Blaming unions for such things doesn't appear to be a well researched argument.
Someone who doesn't have or is unable to obtain a job offer with much higher compensation in industry.
For example, hiring a CS or Math grad as a HS CS teacher is more competitive than hiring a French Literature grad as a HS French teacher. The CS grads have a lot of other options and at any fixed compensation you will get much better French teachers than CS teachers.
Why aren't we paying teachers more money already!