that higher G loading on reentry is more likely to have an adverse effect on the Shuttle pilot's ability to land the vehicle. For the capsules, the deceleration forces are easier to handle because the astronauts are sitting roughly parallel to the heat shield. This lateral (or is it transverse?) G loading is the easiest way for the human body to handle high Gs because it doesn't drain blood from the head.

If the Shuttle reentered in an extreme nose high attitude, the forces would be perpendicular to the pilots in a sitting position. This is called positive G and is similar to a fighter pilot during maneuvering. You'd either have to have some form of reclining pilot seat or some really good G suit to sustain a high positive G load through the entire reentry deceleration phase and then land a vehicle with the glide ratio of an anvil. All the capsule pilots have to do is maintain proper attitude during the reentry and to ensure the parachute deploys on cue.