Indeed, the end-of-year school disco has in many places morphed into the type of elaborate do that you describe, along with the extra huge expenses that it brings with it.
I still have no idea what "homecoming" means, despite hearing the Monkees singing about a homecoming queen (whatever that is) many decades ago.
While we're on stupid American customs, I have noticed one that has recently been creeping over here at weddings. That is for the bridesmaids to precede the bride into the church. How fucking ridiculous. They are supposed to be there to assist the bride, to carry her train. They are no use walking in front of her!
Last Christmas I watched a bride going into church on a wet and windy day. She had to lift her dress right up and all but tuck it into her knickers to keep it out of the mud and puddles. If they had kept to tradition with the bridesmaids following her, they would have achieved this in a far more elegant way.