This is one of the biggest misnomers to be applied to any type of new technology. The idea that a machine attempting to emulate a human being can further "humanize" its output is absurd. The machine is doing all the work -- there is no human beings involved in "humanization." Thus a more proper term would be "shitifier" as it makes output more shitty albeit in a very robotic way.
I can't find back the post, but I saw someone describe it as posts having a metalic taste. You don't need AI detectors to know something's off with a post, but it makes it easier to be convincing.
Most of the time I can't get myself to read AI output. It just feels wrong.