It's not just that - it's what the software needs to do. In order to block swords but allow for a fondle of an assimilable console or a grip on the victim's shoulder, the defensive routine would need to raise and drop the kinetic-barrier shield again and again, sometimes very rapidly. Not only would this interrupt important operations, it might be very hard on the shield-generating hardware.
It's all fine and well to erect a slab-sided beam-blocker some distance away from the Drone, as in "Q Who?" and other TNG eps, as long as this doesn't prevent the Drone's hands from assimilating the interesting console. But a shield intended to defeat close-and-personal sword or fist attacks would deal with a different, more mobile situation, and might hinder operations too much. If the Drone could isolate itself inside a largish shield "greenhouse" good against all threats for the duration of its mission, that'd be ideal. But it may not be practicable.