Nate knows that he'll be the underdog against every top 5 lightweight and that a loss against one of them would diminish his stock significantly. The only thing he's got and ever had going for him is his victory over Conor McGregor so he'll hold onto the chance to get a massive payday out of a rubber match with him before he'll either retire or go back to his status as a glorified journeyman in the lower half of the LW division rankings. Don't get me wrong, I don't blame him for that, it's the smartest thing he could do right now, it's just that he's clearly overestimating his own value. He's not the value in this fight, the whole story is and always was big draw Conor fighting against the first guy who beat him in the UFC. If anything this fight became less interesting and less valuable after Conor now lost to another fighter in the octagon, one he shares a much more personal and intense rivalry with. The only reason I see why Nate suddenly took the fight with Poirier after turning all those fights down is because the two would match up similarly as McGregor and Diaz and given the fact that Poirier is most likely still not on the same level as Conor Diaz might've been hoping to be able to push for the trilogy by beating Dustin.
If we never see Nate Diaz in the octagon again, I honestly couldn't care less. The guy's antics have become more than annoying, he's never been as exciting in the octagon as his brother and the last thing I want to see is the UFC giving more people spots and shots that they've earned through talking and fan support rather than through their accomplishments in the cage.