To come back to this Air Asia case, I have seen no indication so far that the Pilot of this flight did not jut do that, but he did not tell ATC, so for me I think there must be something else, or the initial request to deviate came much too late.
Late, I might agree, but I think there was something more (or more subtle) than that?
E.g., perhaps they unknowingly deviated
into more severe weather, or got caught in a newly developing cell -- and
then an still-unknown event (pilot error? systems error? structural failure?) became the probable cause of the accident.