People can pay for whatever they want to see her in. There are is a hundred different ways to be a fan. This play is not selling because it's not a well known show and she is not singing. Everyone I know who has discussed it all say the same thing. Two top actors but nobody cares. Do the math.
Frankie and Johnny, released in the midst of Tony season with a lot of strong competition among plays, may not work at the box office because Audra McDonald doesn't sing. We'll see what happens after the reviews.
I saw it last night. And while I was ambivalent about the play and still mulling it over, McDonald is wonderful. I'm certainly not telling anyone how to spend their money, especially after I got a $25 deal to sit in the mezzanine. But there's a market dislocation, which seems like it has created an opportunity for people who admire McDonald to see her giving a compelling performance - for the price of a rush ticket.