[rst]

For one thing, the trajectories are very different -- New Shepard is pretty much up and down, while the SpaceX booster's velocity is mostly horizontal at stage separation; it requires a substantial amount of maneuvering to cancel that out. For another, SpaceX's landing attempts have been on a barge, not flat land, which means that targeting is a much harder problem. (The latter is speculation on my part, but the New Shepard booster went through a lot of gymnastics just before landing; that sort of thing can be a whole lot easier if you just have to wind up level with zero velocity, without having to target a particular spot on the ground as an added constraint.)

EDIT: some observers claim that the New Shepard is hovering. If so, that does two things: first off, it indicates that either the stage is ballasted, or Blue is taking advantage of their engine's very deep throttle range. (SpaceX's first stage can't hover, as even fully throttled-down thrust of one engine exceeds weight of the stage at landing; so long as an engine is firing at all, the stage is accelerating up.) Second, it obviously makes the targeting problem much easier. (Note that the ballast could just be extra fuel; they've clearly got extra to burn in the landing maneuvers...)