This paper generates an interesting research policy question: Why was Exxon able to create equal or better projections than the NASA?
Focus?
Climate change, and the elimination of the use of carbon fuels (oil), would potentially existential threat to Exxon, so they better know everything about it. NASA has a whole bunch of things to focus on in addition to climate.
It's substantially smaller than Exxon Mobil's. (Plus, some of Exxon's budget went to casting doubt on others' research.)