People say this like it’s a new trend.
The reunion auditions follow the same process as the open calls. Basically, it’s all luck in who gets cast and who doesn’t. The casting directors don’t know or care all that much about who is standing in front of them. They have a list of the role dimensions they’re casting for (costume sizes) during that round of casting and if they like you, you’re in. It’s an assembly line and a calculation.
Now, they cast to a number. That number includes two full casts for houses and zones, three-five swings/fire crew for each, and then enough back-ups for a third of the total number of performers they need for a night. They can’t predict quits, or call-outs, or the number of back-ups that show up each night for roles.