The not entirely voluntary audience

From The Great Mutiny by Christopher Hibbert. Page 36.

After tiffin most ladies went to rest during the hot afternoon, rising in the early evening to dress for the essential parade of carriages in the Mall (or whatever the area selected for this ritual happened to be called), the visit to the bandstand, the formal dinner, or the performances at the theatre, which usually consisted of three or four short one-act plays as these not only provided more parts for the officers and ladies who wanted to take part but also, so it was sup- posed, proved less tedious than one longer play for the not entirely voluntary audience.