Humans also usually tend to buy the products which they have been repeatedly exposed to more than other product. Repeating is very important for advertisement. For example. Product A has not been advertised and Product B has been advertised. When a consumer is exposed to a product a lot, in any way possible (video, poster), they tend to buy product B, the product they have seen more, instead of product A. Because it seems familiar, they know more about the product and they would think it's worth the shot (and the money) to try it/buy it. Ask yourself: You have to choose between two of the same products but a they are from a different brand.. Would you buy the product which you have never seen before or would you buy the product which you have seen in a poster or a video?

They want to attract a certain group of people to the product in hopes that they'll profit from it.

It's like debuting a new group. What if there were no photo/video teasers for members or the music video? What if the company just announced that they were debuting a group on a certain date and expected us to anticipate it? Listeners would have no knowledge on the group's members, or the concept, or the purpose of the group. We would be in the dark about every detail of their merchandise and everything. Nobody's going to want to "buy" the company's product if there aren't teaser to create a fanbase and a general profit. So that's why companies advertise via videos and posters.

Visual attention. And for those videos, poster that has info, people can refer back if they wanna know more about it.

It attracts people's attention more than just the product itself.