An article from The Atlantic states that reality TV shows cost considerably less to produce than scripted TV shows. Because there is such a low budget, many stations run multiple reality TV shows, as revenue from sponsors pays for the show in a short period of time.
Because reality TV shows are unscripted, subject matter and events arise that producers cannot predict, such as somebody being punched in the face at a bar. Scripted TV shows have more control over the content, and can sometimes lack the "surprise" factor that reality television has.
Reality TV allows audiences to see real life, and all of the drama and joy that comes with it. Viewers often get attached to programs to see how their favorites fare in competition, whereas others enjoy watching pleasure from another's misfortune.
Reality TV shows are under constant criticism for not actually being "real." Sometimes scenes are re-shot due to malfunctioning production equipment, which makes the work "staged." Editors often reorganize footage to create more dramatic story lines or conflicts.