#3 Use your heads, Sasha and Seth
It is a common sight in all multi-man matches in WWE, to see temporary alliances being formed to take out strong competitors, and more commonly, friends who are united in the beginning, only to turn on each other at some point, with the commentators reminding us that it's every man for himself and that this was bound to happen.
The same happened today when Sasha turned on Bayley, and Seth Rollins turned on Roman Reigns. If the match happened to be a triple threat match or another match where the first one to get a pinfall is the winner, this is totally understandable. But this was an elimination match! Rollins and Reigns could have easily teamed up till they eliminated Braun Strowman, similarly, Sasha and Bayley could've continued working together till they could eliminate Alexa Bliss, assuring a Championship for one of them.
It made absolutely no sense for Sasha or Seth to turn on their ally when there was one more common enemy across the ring from them!