The simple compositions and large fields of color were heavily inspired by Russian and Ukrainian movie posters from the 1920s-40s. The rough texture harkens back to the feeling of the "old west" that Westworld tries to perfectly recreate for their guests.
I couldn't help but make a second option that is tailored more towards people already familiar with the show. In the poster above, there are two recognizable main characters in common positions. Lined around them remain the same assembly line figures, constantly reminding of the inner workings of companies like Westworld.