The Diplodocus may not be the best known dinosaur, but out of all the Sauropods, I'd say it's fairly popular. One reason why it may not be as popular as the other creatures I've mentioned before is because it has never appeared in any Jurassic Park/World movie. However, the public likely still has an idea of what they look like and how they behave, but this idea may not be the most accurate anymore. One thing special about the Diplodocus is its extremely long tail, which some think of as a sort of whipping weapon against predators. However, the more general consensus among paleontologists is that it was long as needed for a counterbalance to the heavy weight of the neck. The Diplodocus has been believed to keep more of a horizontal stance than other sauropods (like the Brachiosaurus with an extremely vertical posture) with a long tail that counterbalances the heavy neck. Without such a long tail, the center of mass of the diplodocus would be more towards the head, causing balancing issues. Now, compare my up-to-date version to the Jurassic World Evolution's depiction, why do you think it looks like that?