It wasn't about Luke at all, which Bail realized. Obi-wan is afraid. He's not the hero anymore. He's a broken, frightened and traumatized survivor. He was using Luke as an excuse so he wouldn't have to face that fear.
As for the secrecy over Leia, Bail answered this in the episode. The massive response would draw attention. Leia is nominally an Imperial Senator's daughter. The whole Empire could be brought to bear. But then people might look more closely at Bail's adopted family. Leia's secret is too big to risk. If anybody looks into things and puts two and two together? Daddy comes calling. It's effectively the end of the world.