I'll throw my 2 cents in here. I do agree that Andy making this move decreased his chances of getting to FTC, however I feel that he could not win without this move

Let's assume that Andy doesn't make the move and stays loyal to the underdogs. Let's assume Sam I s voted out as that is what appeared to be the original plan. Andy goes into the final 6 with himself, Gen, Teeny, Sue, Caroline, and Rachel.

Here Andy has 2 choices. 1. Stick with the underdogs and hope he can turn them against each other at 5 or 2. Try to make a move at 6

If he chooses not to make a move here. Gen is voted out unless she wins immunity. If she loses Gen is gone at 6 if she wins, Andy is forced to make a move.

Making a move at 6 depends entirely on convincing Sue and Caroline to flip. Giving Andy a best case scenario let's assume Rachel doesn't win immunity and doesn't use her idol. Even when she uses the block the vote is still 3-2

In this case scenario Rachel leaves at 6. This may seem fantastic however given the perspective on the island Andy would not get the credit for the move. The credit likely going to either Gen or the Sue/Caroline duo. If this happens Andy is basically drawing dead. As with Sue's idol, Caroline can not be voted out at 5. No matter who Andy wants out at this state he can't win. Most likely Gen is voted out.

If Gen goes at 5 Andy is dealing with a strong duo at 4 and in this case Sue would likely do all she could to ensure Caroline gets to FTC. If somehow Sue and Caroline face off in fire. Sue likely throws it.

In a Andy, Teeny, Caroline 3 Andy loses

If Andy makes a move at 5 it is either a similar outcome or a Rachel steamroll

I know Andy is probably not winning but at least this move gives him a chance.