Starfleet, and perhaps a number of Federation officials, could well have reasoned bringing Khan and his group back into society was a risk they weren’t willing to take. Rehabilitation was probably considered highly unlikely. As it was they could well have figured Kirk’s action wasn’t a bad idea after all. And Kirk didn’t try to hide it. Indeed he did the smart thing in getting them off his ship ASAP. Kirk might also have thought it was too risky delivering them to a Starbase so he parks them on Ceti Alpha 5 and tells Starfleet who tell him they will deal with it. Or not as it turns out by deciding to leave Khan where he is.
And who knows? Maybe Starfleet was monitoring them periodically from a distance until they saw Ceti Alpha 6 explode and shift Ceti Alpha 5’s orbit therein laying waste to it. Note from orbit the Reliant barely detected any signs of life. From a distance scans might not have detected any survivors so they assumed everyone was dead. At some point Kirk might also have gotten word about what happened and accepted the notion Khan and company were most likely all dead. So he files that away and goes on with his life.
Khan’s idea that no one was checking up on them is flawed. It’s as if he expected people beam down to check with him personally. But why would Starfleet or anyone have to risk that if they can scan from a distance? Everyone on board Reliant was safe…until they beamed down and were captured.
And who knows? Maybe Starfleet was monitoring them periodically from a distance until they saw Ceti Alpha 6 explode and shift Ceti Alpha 5’s orbit therein laying waste to it. Note from orbit the Reliant barely detected any signs of life. From a distance scans might not have detected any survivors so they assumed everyone was dead. At some point Kirk might also have gotten word about what happened and accepted the notion Khan and company were most likely all dead. So he files that away and goes on with his life.
Khan’s idea that no one was checking up on them is flawed. It’s as if he expected people beam down to check with him personally. But why would Starfleet or anyone have to risk that if they can scan from a distance? Everyone on board Reliant was safe…until they beamed down and were captured.