A lot of them love that he "tells it like it is," even when he's spouting nonsense. They've noticed that inoffensive, press-release-style messages are often bullshit. So they believe that someone being a jerk must be telling the truth.
They listen for keywords and if the rambling speech has them then it's a match and the speech was a success.
Trump was a build your own candidate. He said so many things you could pick what you wanted and ignore the rest as pandering to get votes. Turns out he probably was always pandering.