I am not sure it is fair to blame us American's. I have never heard of a Christmas Eve box until this thread and had to Google it.
When I was a child, my parents would allow us to open one gift on Christmas Eve. It was not an extra gift, we would have one less on Christmas morning.
I started buying pajamas for my kids to open on Christmas Eve. There is no Christmas Eve box though, I use reusable gift bags which are put away each year.
As for the jammies themselves being a waste, I would always be sure to get a print that would my children would like year around. My oldest loves Christmas and has a tree up in her room the entire year, so she would love Christmas themed jammies. I would think that each family would know the children enough to know if Christmas themed jammies would be worn year around or not and buy appropriately so there is not waste.
All of my children's clothes are passed down through several neighbor kids as well since my kids are the oldest on our street. My neighbor laughs that she has not had to buy clothes for her kids in 8 years, she just waits for me to pass them down.