Everyone is trying to serve their own interests here, I don't think anyone believes that politicians like Donald Trump for instance really truly care about what happens to refugees whom he has never met. Especially Muslim refugees in the case of Donald Trump.
China wanted a "win" just like with the Kokang issue, by using diplomatic pressure to reach a compromise with Myanmar. Giving them a face saving escape route that they could play as a "win" for their domestic population.
However, after the USA + Bangladesh have splashed this issue all over the world, turning it into a giant international issue, the Myanmar government now cannot back down without looking like they have lost face.
Imagine what Donald Trump and Bangladesh would say if Myanmar backed down? They would wave it all over the world as their own personal victory (regardless of what actually happens to the Rohingya), while Myanmar would look like it has backed down under US pressure, which is a death sentence for their government, since they would lose the support of the rest of the country.
They have put Myanmar in a corner from which they cannot back down. What kind of diplomacy is this, I don't understand it. They have doomed the Rohingya to improve their own political support base. And they are playing the humanitarian fiddle as if they were actually trying to help them all along, it is obscene.