[pmoriarty]

There's a lot of poor writing in philosophy all around. Passive voice is far from the only authorial sin. Dryness, obscurity, long-windedness and lack of engagement with the audience are probably the most common.

This poor writing is certainly not limited to any particular philosophical discipline, or even to philosophy in general. Math and science tend to be just as bad (often even much worse, except sometimes on the issue of clarity -- at least as far as their intended audience is concerned).

I think the common laborous style comes from the desire to seem "objective", the tradition of presenting very long, drawn out arguments in a "logical" fashion, and the attempt to efface the author from the work (so as to make the argument seem to be self-evident given the premises, and not at all biased or based on one person's experience or opinion). That's hard to do in an engaging manner.

More recently, the practice of revealing who the author is and where he stands is starting to become a little more common. That helps to make the writing more engaging and helps the reader to make more of a connection with the author, but I think this still is very much a minority style. Most of philosophical writing is still mired in "objective" style, and it's difficult to foresee when or if it'll ever make it out.

PS: I'm guilty of this myself, and should really take some writing courses! :)