Friendly reminder that if Milo and co. hadn't shown up at Sub-Terranus-Terranus-Terranus, then Dave and the other Undergrounders would never have left. Why do I point this out? Because I was just watching the episode "World Without Milo". And when Elliot yells out "Let safety reign!", Scott opens up a manhole to see if it is raining. Remember that in this timeline, Milo does not exist. Which means the Undergrounders were never rescued, which means they are still all -- you know -- living underground.
This means one of two things. Either:
1. Scott and all the Undergrounders know how to get back to the surface and just refuse, or
2. Scott knows how to get back to the surface, but keeps this knowledge from the others.
Take your pick. Both are equally chilling in my opinion.