The sea turtles are not laying their eggs, I have already reproduced several and none of them carry out the action of laying eggs on their birth beach, they just have a bigger belly showing that they have the eggs and swim randomly. But don't put them in the sand. And to confirm in creative mode, I put a sea turtle egg in the beach biome to define their birthplace, I waited for them to be born, I made them reproduce among themselves and even then. None of the turtles laid their eggs on the beach where they will be born. They just went back to swimming randomly.