Most of the time, getting through school felt like a boring grind, so it's no surprise that the staff would think of fun themed days to make things a little livelier.
Over the years, I can recall us having wild hair days, pajama days, and days where we dressed up like people from different decades. At no point, however, did any of us decide, "Hey, let's all dress up like cultural stereotypes."
Maybe it's because we were a pretty multicultural school and knew which friends we would make uncomfortable by doing that or maybe the thought just never occurred to us.
However, both that decision a similar one to dress in out-and-out blackface obviously has occurred to kids at a disturbing number of schools and one recent case suggests this problem is no closer to going away.