^To understand the most important thing in reality TV shows or any other business, is to understand the business itself.
People think that their skills are the most important thing that keeps the organization running. But this is true only from the people at the higher levels in the food chain.
For eg: Many software engineers I have worked with have developed a feeling that they have superb coding skills and that their organization could not make it big without him. I don't question the coding skills, the superiority complex is questionable. I have learnt that code is not even 5% of my business. 75% of the business in attractive UI, sales and marketing, etc.
In the same way, the contestants and the judges are just 10-15% of the whole reality TV shows business. No judge or contestant is indispensable. If one wants to leave, another one is readily available.
Remember, its business and its most important aim is to make profits, and also talent hunt as an social responsibility and value-addition.
Imagine how plain and boring the show would have been if the contestants just stepped up on the podium, sang their song, the judges gave their comments and then turn of the next contestant.
I may be wrong, but you seem to a "hardcode" programmer. I have come to believe that the programmer's psychology is that "code and functionality is more important than eye-candy UI", whereas the designers' mind says "Design is the most important". Unless you write programs for the "command-line generation", you know how both are important, and more important is actually selling the program and generating revenue.
Apply the same to these reality shows and you will realize whats it about!