What was the role they wrote specifically for Freeman?
Here's what Rogen said according to Yahoo Movies UK:
"Morgan Freeman said ‘no’. We wanted him to play God. Apparently he takes his character as God very seriously."
Co-director Goldberg added:
"The joke was, he would appear as god, and Jay (Baruchel) would say: ‘so when we were in ‘Million Dollar Baby’, you were god?!’ and then god shows up and says ‘it’s just a joke him and Morgan Freeman have been playing on people. He should have said yes!"
"I think it’s the biggest mistake Morgan Freeman ever made!"
Maybe Freeman just didn't think the joke was funny. Or maybe he's over the God references with regards to his multi-decade, multi-role career.
This is the End sees Rogen, Baruchel, Jonah Hill, Craig Robinson, and Danny McBride play versions of themselves, who take refuge in James Franco's house during an apocalypse.