Alternate possibility: Earth-1's DEO is *much* more aggressive and effective at discouraging alien migration than Earth-38's.
As I already alluded to, Earth-1 doesn't have a DEO, or at least hasn't had one in the past. That was made explicit at the end of "Invasion!" two years ago, when Supergirl mentioned to "Agent Smith" that she'd been talking to his boss the President about founding an Earth-1 equivalent of the DEO, as a better alternative to his sadistic rogue operation.