When Kirk was speaking to Khan from inside the Genesis Cave in Star Trek II: The Wrath of Khan, Khan beamed out the Genesis Device. He then said he would leave Kirk marooned inside the barren planet, Regula I. Buried alive.
It would have been smarter to beam up Kirk and everyone else to the Reliant rather than leave a chance for Kirk to escape. Khan has no idea whether there is any communication equipment inside the cave. If there is, any Starfleet officer would just contact call for help. Starfleet would dispatch dozens of ships to pursue and destroy Khan. Surely a genetically endowed superior intellect would have deduced the outcome.
Why did Khan leave Kirk with a chance to escape?