It's a transitional period. Hardcore players can now finish the raid in a couple hours but a Sherpa run with new players takes significantly longer. Sherpas will be more common in a couple more weeks as those active players gear up. For now, what I do is just post that I'm "going for Golgoroth" or start at a later checkpoint. You'll just have to run it piecemeal for now. Make your own groups and jump into any checkpoints that will take you so you become familiar with the encounters. I haven't killed Oryx myself but am not upset that LFG is being selective. I totally understand.