Jack Nicholson is not having memory issues. Watch About Schmidt - observe the level of acting in that film by Jack. He wanted the Oscar - and it was his last push... that was a tough role to take. He played a character 180 degress off himself.
Do you think he needs a script to act?
No, the reason he pitched that idea is because if you look at his last two films, they were forced.
Bucket List was a money maker. They probably, initially, wanted Freeman to be the rich guy.