The gear's not designed to be raised in a 3g turn or
The PNF is so sh1t scared that the jock in the left seat is going to scrape the left wingtip thru the foreshore that he forgot to pull the gear up or
There is an AD out about gear doors falling off when in transit, and therefore must not be retracted until WELL over the water, and in the case of CNS outside 10DME so they don't land on a charter boat or
Airbus pilots are unable to do more than two things at once or
They wanted to make doubly sure they didn't pull the flaps up first!