There are two things happening here that will overwrite the choice to select human for target for
Curse of Death's Hold, tested only with preferred_controller = 1-player added although I expect the same results without it.
One factor is the low AI life (1) and Human's creature at 6/6. Fact - Give AI life bigger than 4 and AI will curse human. Assumption - AI after it's evaluations sees that if it plays it on opponent Human's creature goes to 5/5 then play
Death's Approach (with one creature on humans grave) on it and goes to 4/4 so with more than 4 life AI is safe next turn.
I think it is a matter of AI tries to protect itself from Humans next turn and some De-synching. AI has 1 life and
Blessed Orator in play it's code forces AI to attack with it's only creature, [ AI will attack with any creature with power bigger than 0 if it will not die in combat (except some mana creatures sometimes, and those that can't attack of course, and sometimes also with creatures with banding)]. Assumption - AI sees that and it plays
Curse of Death's Hold on itself so it's
Blessed Orator goes to 0/3 power and now AI is no longer obliged to attack an has a blocker for next turn, still a 0/3 can't stop a 5/5 creature with trample and not loose that's why I mention that AI could be de-synching or just not taking into account trample damage. This assumption is based on the fact that if you give AI another blocker like a vanilla 1/1 for instance AI will cast
Curse of Death's Hold on opponent and of course attack happily with
Blessed Orator.