Case study : France 1975-2008
This just means that since 1975 the number of screens keeps growing, globally, but the auditoriums tend to be smaller, containing less seats each, maybe with wider seats, more comfortable (or more space reserved for concession stands). So more screens (not that many more though) to show more films, but smaller audience for each film. It's also the slow decline after the boom of the 50-60ies. Fewer people go to the movies now than they used to back then. The admission price has dramatically increased in the meantime (an average of +7% per year between 1960 and 2000).