Most importantly, everyone looks up to Arthur because the filmmakers need them to. Why? So they could launch the friggin' King Arthur cinematic universe. Of course, the movie didn't do well enough to spawn any sequels, despite the Arthur character becoming an instant icon amongst the people. Though, again, they may have simply been afraid of his magic sword.
Similarly, when Jennifer Lawrence's Mystique shows up in X-Men: Apocalypse, she's treated almost messianically by the gaggle of superpowered students.
20th Century Fox
20th Century Fox"They look up to you."
20th Century Fox"I am the Lawrence!"
Wait, they "look up" to her? She betrayed the guy who runs their school and became an assassin! Why does everyone find that admirable, exactly? The real reason might have more to do with the fact that Apocalypse was Lawrence's last contractually obligated X-Men movie. It makes sense that the filmmakers might want to artificially inflate Mystique's importance to keep her around.