When did the term "whitewash" start meaning racist and stop referring to censorship or covering up of the unsavory? The English language is great at coming up with new words,we need to stop repurposing old terms with well defined usage.
The great benefit of mirrors is that they preserve depth perception, and furthermore you can move your head slightly to get a better angle to view something. In short cameras suck because of loss of parallax.
One reason I can think of is that journals offer a sort of legitimacy, both through peer review and having to uphold their own reputation. There's no reason this couldn't be done with open papers as well, but there would have to be some sort of organization to the process.
Your number seemed very low from my experiences, so I took a look at your link and found this:
"According to recent studies, the difference between student-teacher ratio and average class size in K-3 is 9 or 10 students "
So in reality it's closer to 30 kids per classroom.