Timfuhang's explanation is basically correct. In addition, it is a rational way for merchants to adopt price discrimination in order to increase marginal profits by selling tickets to Lao Zhang at half price in cinemas. Because movie tickets are time-sensitive, if the performance is not full, the unsold movie tickets are worthless, but if you sell one at a low price one minute before the performance, the added cost is basically zero, and the whole fare is almost a profit. The marginal cost of popcorn, a product with no time limit, is fixed (not close to zero), so it may be unprofitable or even loss-making to adopt price discrimination.