Not only CPC is a legitimate government, but it is effectively supported by the West. Do you mean that practically all governments of the world have agreements and deals with an illegitimate entity? They would be otherwise collectively gilt of making ilegal dealings.
Deals are made out of practicality. For instance the US did deals with Osama Bin Laden once upon a time. Doesn’t mean anyone wants them taking over a country that has a democracy. If ROC wanted to join China, let them vote to elect the CPC, eh?