Because they're exposing some inner secret, some intimate thing, which is usually confided in only with those closest to them
They're exposing it before a poorly-lit crowd, of thousands of glistening eyes, millions of views in the case of the internet
The storyteller tells stories which are close to their heart, intimate, emotional, vulnerable
But they tell it to the masses, with whom they could never actually have an intimate relation (Dunbar's number)
This inversion of intimacy, this bare exposure, like an open heart surgery
This is what the artist does before the crowd
The limelight is a totalizing, horrifying, dreadful powerful force, which destroys the weak
Most people should lead humble lives because they could not mentally and emotionally bare the horrors of being recognized at an intimate level by the masses
Even the artist, the actor, the TV personality has a hidden side to them, shown only to their friends and family, etc. but they must still feign intimacy to the audience, to appear personable and approachable and friendly
Otherwise they'll come off as cold, impersonal, which is bad for ratings. They'll be replaced by a psychopath who can pretend to be personable while staring into a glistening black lens of the camera.