I think people (not you) expect this to be like a movie, where some crafty serial killer hides a body with care and precision and only very subtle clues.
The truth is much simpler. JM is (allegedly) a serial rapist and killer in real life. This isn't Hollywood. He was already seen on video tapes the night of the disappearance, was careless enough to be seen in 2005 so that a stunningly accurate sketch was produced, clearly left some forensic evidence in at least 3 cases, took the police on a high speed chase, and was dumb enough to try to hide his massive self on a beach in Texas.
I don't understand why people would think that he had some sort of careful solution to hiding a body. I think his MO is to rape and then as quickly as possible dump a body somewhere that he thinks is abandoned. That's all.