My theory - here goes. NBC wants to make sure they will not have to pay out Erin the $2mil. They cleverly convinced her to give up her first $1mil with enticements of double or nothing.
Firstly, they (NBC)want to "use" the "I'll take the money and run" group of men by offering money to go before being eliminated. Hence, the twist next week. Then Rob shows up in 2 weeks time and disenchants those hardy souls who might choose Erin over the money by telling them about Erin's having been there before (which means she has been lying to them) and that her motiviation is money and not love, i.e. she gets $2mil for whomever she chooses and they only get $1mil (remember at this point the men still think they get Erin and the money). The men cannot tell Erin they know. Those who "might have" chosen Erin now know that she lied to them and that she is using their possible affection to get twice as much money as they will get - money grabber Erin.
I understand from another site that when Rob shows up in 2 weeks time there will not be an elimination that night (check out NBC FLOM2 website). By the time the remaining 4 are whittled down to 3 and then 2 when they are told about the choice of Erin or money - no contest. The money wins and Erin gets her consolation prize.
NBC just saved having to pay out $2mil and kept their ratings up over the summer with minimal payout.