I never understood why there were carapacians on alpha earth since there was no reckoning, therefore no meteors for carapacians to be exiled on, right?

Carapacians are independent of Meteors to become Exiles, they go on ships through the Portals, which could still pop up from time to time. There’s also at least two meteors that do go through the Alpha Session portals- The Troll’s Meteor and the one with the Frog Temple, so there’s ways here and there.

There’s also the chance the Alpha Earth Carapacians aren’t even from the Session and are actually like. Part of Condy’s Genetic Experiments.