I know this sounds cliche, but the Royal Rumble is just different from other shows.
It's the only show on the calendar where a world title is not defended in the main event.
It has made a basic Battle Royal one of the most looked forward to events of the year.
Then, when you add what's at stake—a main event match at WrestleMania—you know it's a show that is truly one-of-a-kind.
WCW tried to duplicate the Royal Rumble's success with World War 3, but made it into complete cluster-you-know-what.
The Royal Rumble, outside of last year when they made 40 men to try to spike pay-view-buys, has remained mostly the same.
Despite being the same, you can remember each event distinctly.
WWE has so many pay-per-views they tend to run together, but outside of WreslteMania, it's one that always stands out to people because of its uniqueness.