I wonder how soon Smyly might actually pitch in a rehab game? They may prefer having him just do BP type throwing, because maybe the competitiveness of some of these guys just takes over in a real game, even if it's in Mesa, and they want to avoid that for now?
A rehab assignment, I think, is limited to 30 days, right? So they probably wouldn't have wanted to initiate that in July, even if he was maybe ready physically, because if the rehab calendar runs out, and it turns out he is NOT ready yet (whether physically unready or maybe he's just fine physically but he's got Chatwood-level control.....), then you're stuck.
But if they started a 30-day rehab now, even if he wasn't ready there would still be plenty of 40-man space once the rehab expired, so the only risk is to bump guy #40 off.