Well, people don't see the world as you do. They don't/can't see they are giving more information to Facebook by liking a brand. They do it because it's a way

Well, people don't see the world as you do. They don't/can't see they are giving more information to Facebook by liking a brand. They do it because it's a way to socialize. Also when you like a page, you will be following it. That is, you will see news from that brand's page on your news feed.