They probably thought the manga design wouldn't sell?
Crystal was a ONA project. Eternal was a theatrical project, so everything had to be more recognizable. Hence why they hired the original character designer and the voice actresses did a job more similar to their 90s counterparts.
I think the new illustrations are quite elegant and lovely, but I don't like the coloring. There's something odd about it, like a poorly lit photograph.
There's also some weirdness on how she's modified their uniforms. I hate the new chokers. Not only do they do away with some of the unique variants (Neptune, for example) but they look like cheap cat collars with those reflective panels to alert oncoming cars.
Also, Pluto, Jupiter, and Mars have lost their custom uniform elements. Weird since Venus still has her chain. There's definitely something about this version of the uniforms that comes across as basic b**ch.
That's not what I mean. It's like they're all cast in a weird, dim sunset. There's an orangey-brown tone to everything, and the lighting in the illustrations (not the photographs) is putting the emphasis on odd places. Just look at Chibi-Moon's face. Her eyes and face are mostly in shadow except for that weird triangle everyone has, and then the top of her hair and uniform are what are lit up.
Now that I look at it more closely, the shading on Uranus' legs is really sloppy.