It's definitely a risk-reward thing. And an age/health thing. Ryu could be as good as any of them but will he stay healthy (and will he even leave LA)? Keuchel still strikes me as Arrieta 2.0, which is a two-way street (Arrieta's been disappointing/hurt but still put up some WAR). Gibson seems pretty mid-tier, once you get to him, there are a lot of other names IMO. You could even argue that at 32, Gibson's future isn't necessarily better than Smyly's (and they both are TJ guys).
I don't know why MacPhail and Klentak always seems to feel the need to try and temper expectations because it never actually makes the fan base happy. But it's also possible the Phillies simply won't be able to sign the Top 4 guys - let's say Cole goes to Anaheim, Strasburg returns to DC, the Mets keep Wheeler and MadBum wants to play closer to home in Atlanta. I'm not necessarily getting in a bidding war with the Padres over Odorizzi (but if he turns into the new Arrieta or Keuchel with no major offers, sure).
Money is our best asset but it's not unreasonable to want to protect the picks too. And while a bird in hand is always worth more there are probably still scenarios where trading three players for a controllable starter would be better than losing a second-rounder for an older more expensive one.
I don't see the Phillies signing two QO guys (no reliever or position player) though so just losing a second-rounder for Cole, Strasburg or Wheeler still a no-brainer IMO.