I've got a theory on why Soa is fighting Potts, so hear me out. In his current run, he's beaten Krylov, who should drop to LHW after he steamed Walt "I'm huge but I'm not actually a fighter" Harris, and he's beaten a stand up guy in Barry.
I'm pretty sure the UFC wants to test him against someone who could be dangerous off their back, because there's not secret to Soa's gameplan.
That basically means jiu jitsu, in in the heavyweight division that means Werdum, Big Nog, Mir or maybe even Napao. They're either booked or just lost their last fight recently.
Potts won't set the world on fire but he is decent off his back, so I'm thinking this is basically a fight for Soa to show them what he's got against jiu jitsu. Problem being, Potts won't be able to take Soa down, and if Soa does manage to get full mount...well it's all over. Next opponent should be 10-15 ranked HW.
Wall was fighting up a weight division against Garcia and took that fight on super-late notice. A full training camp and he should be competitive against Salas - not saying he'll win, but it won't be nearly as bad as the Garcia fight.