I think there is a common economic structure in organization that creates a-hole cultures.
Actors, PhD students, etc. enter into superstar economy where many people compete for very small number of positions with prestige, money, power, fame (or whatever the measure of success is in the field).
Each position with value has large number of potential candidates who are all good enough. It's difficult or impossible to rank the top applicants with high accuracy and objectivity. Those who are selected are receiving something of great value from their mentors for subjective or arbitrary reasons.
Normally you would use auction or some other mechanism to sell the position, but actors or PhD student's don't have that kind of money and selling a position may be seen as ethically questionable because you are supposed to select the best.
The abusive culture is the result of this extra value that is given out for subjective reasons. Movie actors can be expected sell sex to cover the gap between their innate value and the position they are getting, PhD students can be used as a slave labor for years.
To correct the situation incentives should be aligned. If PhD student works on something for 5+ years, it should cost something for the boss. Dropping out from PhD program should cost something for those who are in the position to select who gets in.