That was the original premise of Reality TV, which largely grew out of COPS (which is heavily edited, but still the closest thing to a true reality show), but it didn't take long for production companies to realize that if they could actively participate and increase the level of drama, as well as RELIABLY create drama on a schedule rather than waiting and hoping something interesting happens, then their show would be worth more. Most of these reality shows have a team of writers, producers, and production assistants who manufacture a lot of the drama and do so on a schedule. This creates a "sure thing" that makes networks feel much more comfortable about their ability to sell advertising (and advertisers more comfortable about buying it).
Also, understand that a large percentage of the people in reality shows, especially prime-time shows, are ACTORS (up-and-coming, unknown actors) who sign up for every reality show that comes down the road. Same with cooking shows: there is a pool of "wanna-be celebrity chefs" who try out for all the cooking shows, and a number of them have been in different shows. The media likes to pretend these are all just random people off the street, but that's almost never the case.
The ONLY safe assumption you can ever make about ANY media is that it has been manipulated by the producers in some way. Maybe it's just to increase the entertainment value or the quality, and maybe it's for a more sinister purpose, but NONE of them are simply a camera that's set up and left rolling, with unedited footage being aired. Remember that.