There are several other factors that could change demand for movies. Some examples:
- People's incomes. All other things being equal, people who have more money are more likely to go out to watch a movie. So if incomes go up, demand for movies goes up.
- Price (or availability) of substitutes. Instead of going out to watch a movie, people might stay home and watch a movie on their own TV. The price of things like Netflix would affect their ability to do this. So would the price of really big screen TVs that give a more theater-like experience. These are called competing goods. When the price of a competing good goes down, demand for "your" good goes down. So, for example, if big screen HD TVs go down in price, the demand for movies will go down.
The change in demand does not shift the demand curve. It only shifts the relevant point on the demand curve along the curve, which also changes the price associated with the demand. For the demand curve of a product to shift a change in consumer preference is required because "Demand curves are used to estimate behaviors in competitive markets."
As the product here is movies, this could include factors like whether producers are releasing movies that can attract viewers and make them want to see them. Economic conditions can change consumer preference; when times are good, people would not mind spending time and money on non-essential items like movies; else these would be given a low priority. Factors like piracy can also change consumer preference, if the same movie is available for people to watch for free, they would be less likely to actually pay to do the same.
Apart from this there can be innumerable other factors that can change consumer preference and shift the demand curve. The change in the number of buyers is not something that shifts the demand curve.