Some can argue that they can be created, but it is undisputed fact that audiences do indeed exist beforehand. The thing about many people is that they don’t always know what they want, and that they have to be shown or taught what it is they want.
For example, say you like comedy television shows, but you begin to like soaps. This strikes you and some others as surprising because you wouldn’t expect yourself to enjoy something so different. Audiences set their own expectations, but sometimes they won’t even begin to guess what they expect out of other things.
I don’t watch that much television anymore, so I don’t know what to expect out of most shows nowadays. This presents either a challenge or a blessing to a company or organization depending on their audience’s needs. Some audiences would be happy if something’s just thrown at them, and some will go rabid if they’re not given exactly what they want.