Well, the Karsta Wor-Ul version of the destruction of Krypton dealt with that.
Short version: Krypton's neighbors didn't like them. Shortly before the destruction of Krypton... in an event planned to kill everyone. The majority of the assets owned by the Kryptonian military were recalled beck to Krypton because the Kryptonian god computer knew the planet was going to explode and wanted everyone to die. Yes, this wasn't everyone, but most of the outliers got killed. Karsta was in a sizable group and most of them died. She survived because she ran away and hid.... she came to Earth because eventually she ended up being the one and only member of the group left.