Just like Mayweather carried De La Hoya to cash in on the rematch (which never happened though but that's a different story). Once Nate is in full control of the fight he won't look for the finish but will carry Conor and the judges will probably gift some rounds to Conor, resulting in some split decision and controversy which will pretty much warrant the trilogy fight.
Nate is not stupid, he knows that the fight with Conor is the big money fight but he also knows that the biggest money fight is the potential third fight with Conor, the epic trilogy fight.
He doesn't need to take a dive like some people here suggested. I think Conor will win the first round like in the first fight, 2nd round will be close then Conor will gas in the 3rd and started getting tagged left and right again but this time Nate lets him survive. Nate wins the 4th round but doesn't do much in the 5th round resulting with a close last round which will likely be gifted to Conor.