Original ideas are risky.
Rehashing the same stuff over and over again at least gets viewers who went to see the first one. They're already hooked, and are more likely to sit through crap and even recommend it to friends just because the first one didn't suck. Much - there are of course exceptions, such as Scary/Epic/Stupid Movie.
"Steven has an incredible story in mind for the sequel that will bring E.T. back to earth."
Turns out that Drew Barrymore now has Space AIDS from kissing E.T., and Elliot grew an extra finger from the spot where E.T. healed it.