why mr. kiaga wanted to burry okonkwo? what reasons had he?

Mr. Kiaga and the others bury Okonkwo's body because the people of his village are not allowed to touch it. Okonkwo committed suicide, his body is now considered evil, and only strangers are allowed to touch him. This is why Mr. Kianga and his workers take it upon themselves to bury the body.

but what's the difference with Enoch?

I don't think we're ever given an exact reason, but Enoch has desecrated one of the clans religious dieties...... this would be seen as unforgivable by the tribespeople. His death would be punishment; Okonkwo's self-inflicted.

thx a lot c: