I think Tampa wants to make sure those two guys are ML ready before they bring them up (what a RADICAL concept). There track record says they know how to develop pitching and they usually get it right.
Both Archer and Odorizzi must need a bit more time in the minors, because the Rays sure know how to develop/scout their pitchers. Yesterday, when Hernandez started, it broke a streak of 1,207 games without using a free agent pitcher, I believe. That's amazing. When is the last time a Rays pitching prospect failed? Although not all of these names were drafted by the Rays, all of them have had extended amounts of success at the big league level, or at least appear to start having success at the big league level: Garza, Kazmir, Shields, Hammel, Jackson, Cobb, Moore, Price, Niemann, Davis: it's insane. It was reported that Niemann's velocity was down; perhaps that is the reason why Hernandez broke camp in the rotation. I don't know, maybe I just admire how the Rays run their organization and wanted the young pitcher streak to continue.