For them to change work on the seamless world would take time and resources that barely have at this time. Yoshi and Dev team decided back when the development of this game they wouldn't do the seamless world for the sake of development and also bring this game to PS3 which was also limited and could barely handle the game. But with that System dead we still have the PS4 and PC. Also, Limitation of this current engine may not allow it. OP you make it seem like its easy to do this. But it isn't it requires time and money for a team of coders, Designer, QA Testers, and other people make sure that maps and areas function correctly SE Mangement isn't going focus money on that. I rather see more focus on new content and fixing the servers issues then reconnecting world.