Reasons

Ron Howard directed Akiva Goldsman's adaptation of Dan Brown's The Da Vinci Code, starring Tom Hanks. It was a huge international hit, but reviled by the critics.

Now they're back with what amounts to a sequel, Angels And Demons. I assume the main reason they're doing it is the (mindbogglingly huge amount of) money. But I have to wonder if in the back of their minds they're also not thinking "let's do it again and get it right."