People fall asleep while watching a film because films contain inherent indifference to viewers. Events and scenes flow non-stop and stories develop automatically regardless of viewers' understanding and experience. For example, nobody dozes off as watching a short social media video.
Examine the statement and give your opinion.
It might be said that the independence of films from viewers' situation drives them asleep. The screen shows events and emotions in indifferent relevance to viewers, while short clips on social media never make people sleepy. Although the statement raises an interesting observation, which may explain people's sleepiness during a film, I think people feel sleepy while watching a film for various reasons, and also the example the statement provides does not necessarily support the argument.
First, it is reasonable that the statement argues films are different from viewers. Films are shot and editted by professional production teams, who are different from consumers. Unrelatable stories might leave audience behind. On the other hand, most of short clips on social media are created by ordinary people and felt familiar.
Second, it is debatable about the reason people become sleepy while watching a film. People have different preferences for films. Romance film lovers may find science fiction films tiring. Or people may see a film after work or a meal and find themsefves too tired to focus. Differently though, short online videos are often only for seconds or minutes, so it is unlikely to catch someone fall asleep watching it.
To summarise, the statement may be legitimate, but needs more comparable examples. The comparison with short videos fails to strenthen its validity. I think people get sleepy while watching a film for various reasons, such as being full or physically tired.