'Cause Doc doesn't like to mix things up. We may not have a lot of post players, or great post players, but let's face it: Doc has a specific system that he designed when the Big 3 came together, and whether good or bad he sticks with it, no matter what. This is why we have Jason Terry, a pick-and-roll player, running Ray Allen's multiscreen curl routes. Doc wants Rondo to dominate the ball, he wants whoever's in the "Ray Allen" slot to run around endless screens, and he wants everyone else standing around the perimeter 99% of the time.
Look, Rondo has great court vision and is great at getting the ball to guys where they like to receive it, but to stick to that alone is such a stilted way to approach offense that it always ends up stagnating sooner or later, especially since Rondo doesn't really like to drive a lot and take contact. There's no mixing things up under Doc's system, except that now he might not have a choice.
Bradley, Lee, and Barbosa, and probably Green, are capable cutters.
Sully, and to a lesser extent Pierce and Green, and even KG still sometimes, can post.
Barbosa and Lee can take the ball to the rim, and we've seen Green do this too.
Variation is key to keeping a defense on its heels, but variation is mighty scarce in Doc's system.