Because you use life like imagery and audio non stop porting in front of peoples faces starting from literally the first days of their lives.

You have talking heads that give people the illusion of a person talking to them, building familiarity and friendliness. Heard of celebrity crushes? Ever had a crush on a media character? Ever got your heart racing watching a scary movie? Human brains might understand they are watching a screen on a cognitive level but the flashing imagery and sounds also speak to lower parts of the brain and subconscious forming ideas and even building pseudo relationships with what they see on screens.