Supply and demand, economics at work. The very popular ones do very well, the vast majority of wannabes flunk out and end up waitressing at the Cheesecake Factory like Penny (from TBBT). Same with musicians, sportspeople, novelists, etc.
In terms of worth of work, I would rather give a pay rise to our teachers, nurses, firefighters, police, military and other services which protect and keep our society functioning than contribute to a foreign actor's multi-million dollar lifestyle (and occasionally obscene excess). But I still like to watch a good movie or TV show.