It's because school is preparing students for life, where it would be outrageous to have written notes while presenting or speaking. What's next, someone else writing the words for you?
How exactly is it outrageous? You are there to deliver the message in a meaningful way, not to recite such message from memory. This is no theater or the cinema where you are playing a role and must be entirely authentic as a result.
Sure, literally reading entire thing from your notes in front of your audience is bad form as it fails to build the captivating presentation. It is just distracting for those listening.
But damn if this cannot ever work for the online presentation where the speaker isn't visible.
It's because school is preparing students for life, where they would never have any chance to look anything up, and could thus only use their own memory.
And that "you won't always have a calculator with you" thing math teachers loved so much? Yeah that didn't age well.
Yeeeah that's already being done for a a bunch of IT courses. Check out some of those "freelance work" sites, it's fairly obvious a bunch of those are someone's homework...