The criticism is of course accurate enough. It's even addressed in the books - there is some discussion in the books about "drum sand", but it isn't really elaborated on in the movie.
It's drumsand, a geological feature unique to Arrakis invented for the book. I appreciate that this isn't spelt out in the film but surely an intelligent audience member should be able to deduce that this is a sci-fi concept and not real life?
Fun fact, it actually does come up in the dialogue of part 1 when Paul and Jessica are running for the rocks from the sand worm, just before they meet the Fremen. It's under some of the music/ambience but Paul steps onto some and there is an audible thump before he notes that it's drum sand, so it is very briefly brought up.
It's based on a soft science book about a guy who can see into the future, has a super-computer brain and controls people with his voice. In later book a guy's clone gets his dead memories because he was ordered to kill his buddy. Another guy lives for 3000 years by putting worms on his skin.
It's a fun series with some philosophical themes. I recommend it. scientific accuracy was not a goal and seems beside the point, but it makes sense for a science entertainer to have something to say about it while it's trending
P.S. their plated skin is involved in their movement. Think it's less a wriggle sometimes and more like a sound wave. compress expand?