It's not even a thing that needs to be known specific to IPCC - this is a side effect of anything requiring consensus between many people, in this case thousand

It's not even a thing that needs to be known specific to IPCC - this is a side effect of anything requiring consensus between many people, in this case thousands of scientists (and politicians?). For everyone (or the majority) to agree to sign their name to it, it must deal with the lowest common denominator.