Right, advertising is a form of disseminating information, but the issue is that there are limited resources to process all this information in the world.
What ads do is forcibly take my attention and direct my resources towards processing their content without my permission.
Sure, I can look away but I need to exert effort (even if it is the slightest bit).
Processing what they want to tell me makes me more informed about their product (as opposed to their competitors) which, if their ad wasn't terrible, will make me less uncertain about it.
This easily makes a number of people more likely to buy it since it will feel familiar, thus making this company better off even if their competitor had a better, but at first more unfamiliar product.