At least that's the oral tradition I've been given in the UK. Makes sense for the old aristocracy, the US may have wanted to make a deliberate break with the tradition?
In the monarchical period of European theatre, it was well-understood that the centre was a _pit_ full of hard-scrabble riff-raff. Having a box apart from this was a sign of social class (i.e. _wealth_ and aristocratic connexions).
If you've ever been to a west-end show you'd be surprised how small the theatres are by modern standards.
There a box is at the side and has surprisingly bad view of the stage. It's to be seen by others. Which is why most west-end theatres don't sell seats in them - you'd not see much. There are exceptions of course.
https://en.wikipedia.org/wiki/United_States_Congressional_Jo...