I think because the response to climate change is economic. It is seen as adding to costs. An economic operator facing additional costs will seek to lower them or push them on to somebody else. This is what is happening in the climate change negotiations. The negotiations are perceived as a sharing of burdens, not of opportunities, not as a response to a common threat.
Economic defensiveness slows down progress.
Climate change is the biggest environmental issue but the global environment is, unfortunately, not at the top of the political and economic agenda. The Convention is a legal instrument that is now ratified by virtually all the members of the international community. It is a foundation, a framework, as the name indicates. It holds States together as they work out a global strategy to combat climate change. It commits them to generate and share information amongst themselves.