Why is humanity still pumping unsustainable levels of greenhouse gases into the atmosphere when all the science points to that being a road that leads to catastrophic consequences which we can't predict?
First, this is a classic example of tragedy of commons - if you lower emissions, then you bear all the costs but a tiny fraction of the benefit; Second, even if coordination can be solved, by and large the groups/areas that can make a meaningful reduction are not the groups/areas that will bear most of the consequences, there's no such thing as a single, aligned direction of interest/benefit for humanity.
I think we can all agree that another mass extinction event and chaotic weather pattern upheavals are both bad things.