why do they still play on the radio when they hate him

They no longer hate on him after his death.
It's just like every valuable thing , you don't get to respect it when you have it and you do realize its importance once you don't have it anymore. But yeah , still some stupid people dislike him. Haters gonna hate you know. No matter what.
Even when he was alive , still his songs were being played on Radio I believe like "Heal The World" , "Billie Jean" etc. No matter how you look at him , turn a blind eye or not. You still can't deny his excellent music.
His music had great messages in it.
:D

Some people hate him and enjoy his music. One of my classmates hate him and talk bad about him but during our school's talent show michael jackson's bad was played and he even sang and danced to it although he hates him.

Like i said michael is de king of pop but thy hate him