Few media are able to hold viewers' attention for more than a couple of seconds (on average). If the advertising objective is simply to show/say something that quickly reminds people of what they already like about the brand, this short dwell time is not an issue. However, if the goal is for the advertising to create new brand memories that make people interested in the brand in the first place, channels like Cinema, TV and YouTube provide an opportunity to tell a longer story that is more likely to be retained in long-term memory and influence purchase decisions for months or even years to come.

See 'The Challenge of Attention' for more details.
Cinema figure taken from here.
Newspaper figure taken from here.
Poster figure taken from here.

What to learn more? Try asking Virtual Dan White.