Nate is a big draw when he's coming off a win, if he isn't it's a regular fight. Jorge vs Nate both were coming off wins and it was for the BMF belt. Prior to beating Pettis Nate's recent fights were vs Conor only and he took a long break so there was hype in his return. Right now he needs a win to garner more hype for a money fight. He's still popular but it isn't the same type of hype when he's coming off a loss.
Poirer's smartest choice is to try and win the LW title and wait for Conor and fight him as the champion. He will have the leverage being the champion and winning the last 2 fights. He gets more money and bigger ppv split. A fight with Nate will not compare to that at all. This would be viewed as Conor's last chance and with their rivalry and a title on the line it could be their biggest selling fight. Their last fights numbers were huge and Nate's fight away from Conor doesn't compare to that. The Nate option is always there for both Conor and Poirer, it's there as their last money fight result. If Poirer loses vs Olivera he still has the option of Conor or Nate. Those options will always be there. But if he's the champion he has more leverage and can negotiate more money for those fights.
Nate has the option of the Jorge rematch, both coming from losses and not scheduled to fight anyone, that's the fight that should be made since there wasn't a clear cut winner from the last fight.
Plus UFC wouldn't allow Poirer to go to 170 just for a Nate fight at this moment, it doesn't make sense. The title fight or the Conor fight is the only thing that makes sense for Poirer to the UFC/Dana. They still need the final Poirer vs Conor fight before trying to do other match ups especially in a different weight class. Best case scenario is if Poirer wins the title and fights Conor as the defending champion. Biggest possible fight they can make in UFC at the moment. No other match up would come close to that in terms of hype and interests from mma community and casual fans.