No, seriously. How many sequels do outperform originals? There are some classic (but still arguable) examples, like Godfather II or Metal Gear Solid: The Sons of Liberty, but those are still exceptions from the merciless rule: sequels commonly lose to originals. At least in originality.
But sometimes there is no other choice, but running a sequel. Like when it is Matrix harvesting too much box office, or the fellowship of the ring hasn’t arrived to Mordor yet, or you have world conquering plans and vowed to go for the Coolest Special Offer Ever. And there has been just the first step yet. It did well, there were lots of awesome two-liners, but the Quest is not finished. And the Grand Offer is still out there, waiting to be found.