The explanations why entertainment folks lean left usually identify two factors: they make their livings via emotion, and they aren’t very bright. That’s too facile. I offer two factors which have more explanatory power.
The entertainment industry is already an uncomfortable coalition between the Business tribe and the Arts & Humanities tribe. Performers are expected to have their primary allegiance to the A & H tribe, and they have conflicts in their daily lives with the B tribe. They are expected to uphold the tribe as much as possible in such conflicts, though everyone recognizes that price is a powerful artistic persuader. When you go to battle for a cause, even in small ways, your loyalty to that cause increases. Note how frequently TV, music and film do unsympathetic portrayals of other tribes – business, law, military, southern, religious - but how positively it portrays its own. If you are an undeniably crummy person from the A & H tribe, you will be portrayed sensitively as a complex and tormented character. The black and hispanic tribes get portrayed as either very good or very bad. They are coalition partners in liberalism, but can be chucked at need for a price.
Many entertainers do not originally come from the A & H tribe. They may be drawn equally from the other American tribes. They are accepted on sufferance because of their attractiveness, talent, and/or presentation. Barbra Streisand has a wonderful expressive voice and is a good comic actress. She is not very bright. Her acceptance early in her career into the A & H tribe would likely have been tenuous. At this point in her career she could probably afford switching to whatever tribe she chose. But loyalties die hard, especially when you have paid something for them.
The explanation that entertainers are not generally intelligent always seemed inadequate to me. They are likely distributed across the bell curve as all the rest of us are. But when someone has extreme beauty or charisma, we look for flaws, so that we might feel superior. Those of us who are intelligent are likely to use that as our judgement point. As intelligence is defined so variously, half the population can provide some evidence that they’re in the top 10%. Thus most of us estimate that Attractive Person X is less intelligent than we are, and are often right. But Glenn Close was a Phi Beta Kappa at William and Mary. Meryl Streep went to Vassar and Yale. They would both be A & H tribe members even if they had not been actresses. Stupidity cannot be assumed. It doesn’t hurt you as much in the entertainment industry as it might in some others, which is why it stands out.