Diaz didn't get an instant shot, he fought BJ Penn then he fought Condit for an interim belt. Though it's fairly clear that the SF HW (both of them), LHW, WW, and LW champions are all in the title mix. But the MW guy, that guy should just be happy to have a job.
Actually Nick did get a title shot. He no showed a press conference and as punishment his title shot was given to Condit who was facing Penn at the time. Then GSP hurt his knee and so Diaz fought Penn, Condit was off the show. He pulverized Penn like a red headed step child and then got the shot for interim gold.
As for Luke I would assume his cast had been removed and he was trying to see if he was ready for a fight obviously not if Bisping gets the better of you.