I think you got it right here "If something goes wrong, we don't know how to fix it, but we may still be held responsible. Most IT practitioners simply won't be able to get over this."
The thing is, IT practitioners make the decisions. Their job is to control the risks and take the responsibility. Until "serverless" evangelists find a way to put that in a black-box, too, it will not take off. And we are far from it.