Assuming the lobsters in the titanic were either American lobsters (or European Lobsters), they actually prefer cold waters are native to the latitudes the titanic sank in. But they prefer shallow coastal areas (usually less than 1000 ft) whereas the titanic sank far out at sea at over 12000ft. The water pressure maybe to much for them to handle at those depths (and even if they somehow escaped before getting that deep, lobsters aren't meant to live in open waters).

Figures that somebody with a username "Cuttlefish" would have such excellent sea creature facts to share.