I think I remember reading somewhere that it goes back to the 1920’s, but that could well be wrong.
Note, this is simply a question. I’m not suggesting that eight a week is “right” or “wrong”. I’m very much aware that things change with time.
The real question is how reducing the number of performances would impact the already difficult economics of the theater. Would an investor’s chances of recoupment decrease? Ticket prices are already so high that it’s hard to see how revenue would be maintained.