They have 25 spots to fill. Only 5-8 of the girls are probably deemed by the casting folks to be likely "matches" based upon what they have learned about the Bachelor's tastes in women, the overall plans for the show's plots/themes.
People like Stacey probably go into the evening understanding that they have been cast to play a role, which upon return to their pre-show life will somehow be a career plus, not a humiliation.
Others seem unable to hold their liquor, and make their own misfortune.
I have always thought (with some reason) that the reason the "Firedrake Firing" has been internally controversial -- and not just with the girls -- is that one or both of those girls was "cast" for a long-term role, and they therefore feel they are deserving of a second chance (at love, at the show, at the public attention, at the "adventure" or some combination of all 4).