Liu Xiaobo is too famous. If he was able to travel abroad his bad treatment in a Chinese jail would be a black eye for the Chinese government. He can and will speak out against China. Therefore he will not be able to leave China. As well, in China he will have limited mobility, sort of like house arrest. Anyone visiting him will be vetted. Reporters of any stripes will be barred from seeing him. China likes to keep their political dissidents quiet.