Both Porter and Danny Garcia clearly ducked Spence. Porter fought Bone and Broner and could have fought Spence for his belt, but he said he was going a different direction, he already had the IBF belt. Then he fought Berto and Grandos, same scenario after losing to Thurman. Spence was available.
Danny Garcia, same thing. He fights Paulie, Lamont Peterson, Sammy Vargus, Guerrero, Rios. Spence was available during several of those fights. They clearly didn't want to fight Spence.
Now, yes Porter is fighting Spence because he pretty much has to.