Why didn't Kansha (Krisna's uncle) simply keep Vasudeva and Devaki separate

Why didn't Kansha (Krisna's uncle) simply keep Vasudeva and Devaki separate so that they could not stay together and thus no child would be born? There are 5 reasons. Reason 1: Kansa wanted to prove Aakashvani, that said Devaki's 8th son will kill him, was wrong. So he kept Devaki and Vasudeva in the same prison cell. Reason 2: Kansa thought it is easy to kill the 8th son on the day he is born. He totally underestimated Lord Vishnu. Reason 3: Kansa thought once the 8th son is dead, he can live rest of his life with a peace of mind. No wonder why he killed the first 6 kids of Devaki. Reason 4: Separating Vasudeva and Devaki would send a message among common people that Kansa is scared of a kid that is not even born. Ego issues, you know. Reason 5: If Kansa separated Devaki and Vasudeva, then Devaki would not become pregnant in the first place. And there would be no 8th son. This would prove Aakashvani wrong. And Aakashvani is never wrong. In short, destiny found its way.