In the case of Rick and Morty, given that the story is a multiverse, any spin off they make can be canon so it's easier to change an art style and plot as part of the multiverses thing.

I know there are purists out there that don't want western cartoon style penetrating the anime industry we've come to know and I get the aversion to change. But anime wasn't the anime we know if we had to compare it with how the golden age anime was and how the art styles we have now are more diverse. I just welcome the changes from the artists that likes to see more art styles in the industry.