Originally Posted by
LineageRazor
Honestly, while not yet confirmed, I think it's being hinted that the Ancients' creation abilities depend on the planet in some way. They might be able to create a spaceship, but once they actually get into space none of their abilities work anymore - which would be HORRIFYING to them. A bit like if we lost our hands upon going into space.
If this is the case, I'd imagine they may have made some initial forays into space, but when they experienced the consequences they noped right on home again.
It does seem that the Ascians are perfectly comfortable on the moon, but that could still be close enough to the planet to be fine, OR it could be that their abilities still work because Zodiark is housed there. If the former is true and near-space is close enough - perhaps they DID. The planet was in shambles near the end, and it's certainly possible that the survivors moved into space while Zodiark tidied up the planet. The creation-depends-on-the-planet thing, though, could still be the reason they never traveled to other stars.