Why didn’t Tom Riddle kill Harry in Chamber of Secrets?
Riddle wants to humilate Harry first, to show him that his powers are no match to his. As he says:
So this is what Dumbledore sends his great defender. A songbird and an old hat. Let’s match the power of Lord Voldemort, Heir of Salazar Slytherin, against the famous Harry Potter.
…Voldemort is the very epitome of a supervillain, and as such, is prone to gloating, monologuing, explaining his evil plan to the hero and then putting him in some death trap that always fails to work. When you simply kill the hero, you are just a killer… But when you mock him first and plan his demise in some fiendishly clever way, you’re truly a villain. 😉