First off, Google is in no way a walled garden. Every Google product makes their data easily exportable to a variety of open source and commercial alternatives. Second, how does the Google system primarily prepare people for the Apple ecosystem? That makes zero sense.

When I grew up in the 90s, every school was dominated by Apple computers, and Apple's walled garden made it so if you didn't have an Apple computer at home to work on homework, you were basically fucked if you wanted to work on or print anything at school. Switching to Chromebooks is exactly what let kids escape from walled gardens, so then they could work on homework using any computer with a web browser.