Schools need to use and teach the technologies that children will encounter in their daily lives, not those that tick an ideological box.
Imagine if schools starting teaching everyone Blender over Autodesk Maya, for instance. We create a workforce where most people will end up knowing Blender over Maya. At that point, there is a compelling reason for enterprises to switch, and we see a world in which Blender becomes dominant and where people will encounter it in their daily working lives.
There are practical reasons to do this - Blender is free so schools pay significantly less, it still has its usage in freelance/smaller companies, and it has a wealth of resources from its large community on learning it compared to Maya. Many free/open source software suites are similar in these aspects compared to their proprietary counterparts. This, alongside the ideological reasons, is enough to switch.
And the ideological part matters too! In the English classes I've taken they regularly teach individualism and critical thinking. Why then, should we take away that thinking aspect when it comes to software and just tell students "use whatever they use, don't question its ethics?"
We have to start somewhere, and there's no better place to do so than schools, where it still benefits the school and students overall to use free software over proprietary software.
But it didn't start that way. It started as an idea and took the next twenty years to become the leviathan of corporate tech today. Somebody had to breathe fire into that idea and spark a life.
When our tooling is open, everyone benefits. We need to learn to look beyond our self-serving natures and nurture unbound software, even if that means a little discomfort now for a greater good tomorrow.