[typon]

Because a lot of people find the animation style weird. I love that movie though

[js2]

The style is known as rotoscoping:

https://en.m.wikipedia.org/wiki/Rotoscoping

A Scanner Darkly was made by Richard Linklater. He used the same technique in Waking Life. Recently, it's also used in the Undone Amazon Prime series (recommended).

[twic]

If we're talking about overlooked movies with weird animation styles based on books by titans of '70s science fiction, i'll mention The Congress:

https://www.youtube.com/watch?v=QHBl43lMJY0

It is, IMHO, better than that trailer suggests.