I think it comes down to money. I remember something abut him at first not being big on being in this film as he had concerns about all the FX and did not want to be in front of a Green Screen the entire time. Then I am sure he saw who was in the cast and of course, they likely upped their offer and he was more than happy to sign on. Films like this can be tricky as although they use mostly CGI vs a mechanical shark, you have to contend with weather which causes all kinds of delays and of course being soaking wet all the time.

They have another one I added to the thread on the target page.