"If you dare to touch her... All mankind on this continent will cease to exist!" (Part 5-Last)
In fact, the main reason why the emperor looked down on the players was because of how weak they were in general, for while it was true that their numbers were overwhelmingly high, only one king was enough to placate whole armies of them with no problem. However, another reason he didn't take them seriously was because when the weak players united to fight the Abyssal Dragon, the emperor didn't see how effective a single skill could be against the Saint grade boss.
By uniting hundreds of thousands of earth mages and activating the exact same skill, these weak players whom the emperor disdained had managed to practically clip the wings of the Abyssal Dragon; a Saint grade boss, thus successfully sealing his ability to fly.