Alright, consider this. All of them are logical. All of them have years of experience, etc.
They know each other. I am not including Foolish and Manifold now, lets look at the Doomsday standoff first.
Techno knows that Phil is non-factor, and that the main problem is Dream.
Dream knows that Phil is non-factor, and that the main problem is Techno.
Phil knows that he can't win 1v1 any of them, not normally at least.
So, the most logical thing for everyone of them would be for Dream and Techno to fight to the death.
Techno hopes that he can defeat Dream fast enough to be able to play catch with Phil. Same with Dream. Since both of them can't afford to go after Phil, since it is hard and backstab-ish.
Phil on the other hand will just wait for them to beat each other.
SBA's state of mind won't allow them to team up in this standoff, it would be suicidal.