I will tell you why people cry....
Most of them have trained since they were little untold hours everyday. Their life's dream is to dance. Here comes this amazing show that showcases all styles and you get to work with famous choreographers. It's truly a dream come true. Most dancers I have known would do it for free, or pay what they could to do it.
So they get to Las Vegas where they are then immersed in this around the clock. They're exhausted, exhilirated and complete nervous wrecks. Dancers for the caliber of this show do dance with their emotions as well, not just the steps, that's a lot of emotion they're putting out there. They want this more than anything in this world. They started auditioning this summer, so this has been a months long obsession. Not a day long audition. If they were smart they started taking classes in all genre's to prepare.
Can you imagine standing on that stage while that judges table analyze you if you're good enough?
I totally get why they cry if they get cut or make it.