E1+S1 : the straight explanation

Everybody has their take, here's mine. After reading a whole bunch of messages and rewatching the ending, I felt dumb for not paying attention to the obvious stuff.

- At 1:18:00, S2 blatantly and honestly tells E1: "Because I love him [E2]. I would rather be trapped here than see him leave with her." Thus S2 truly wants to help E1 get out because she wants to remain with E2 despite everything.

- At 1:25:00, when E2 is knocked out cold, E1 looks at the ladies. The one on the left (S1) seems anxious to leave and is smiling; the one on the right (S2), frowning and disapproving, just stands there, watching E2 on the ground.

- At 1:25:16, as E1 leaves with S1, the wholly immobile S2 remains back with her beloved E2, however badly he might have just screwed up.

Once the realization that S2 wouldn't want to leave without E2 sinks in, everything becomes clear as day. Each Sophie positively decides to stick with the Ethan they've always loved. Simple as that!