When your modus operandi is to turn known quantities into younger, cheaper, and less established talent, it is especially incumbent upon you to be flawless -- ok, that's too strong a word ... maybe unflawful? -- in your choices. That's a lot of pressure, considering that nothing is more difficult to predict than the development of young baseball talent.
The A's don't rely especially on "hitting" with the draft, in that they have seldom kept their top picks. So essentially the A's turn their own young, cheap talent into established "win now" players and turn their established "win now" players into young, cheap talent.