Authorities agree most lawyers write badly. Understanding the causes often helps correct problems; proposed explanations include lawyers' bad reading habits and law schools' bad pedagogy. But the writing teachers now approach consensus: lawyers are just too busy. (See, for example, http://tinyurl.com/6occl4.)
Polishing a brief, however, is not one of the more time-consuming tasks for an experienced writer, since practice brings faster and less extensive revisions. The benefit experience confers in more polished first drafts is easy to overlook, as I did when I didn't account for it in the Disputed Issues entry "Hours." You don't get this benefit by practicing bad writing habits, as advice to forgo style in the first draft prescribes. Best practice is writing the first draft as stylish and grammatical as you can manage while composing at top speed. Rapid composition helps with flow and continuity, while you practice compositional skill.
The writing teachers who make the harried-attorney diagnosis are practical people, but practical aspirations are at odds with their explanation, which doesn't admit improving the profession's written performance. The diagnosis avoids the biggest enigma of lawyerly writing: why doesn't the job market for lawyers force improvement? The weak market pressure for better writing reinforces attorneys' reasoning that their writing must be good enough because it doesn't impede sales.
The best clue about the cause of bad writing across the profession is the lack of criticism lawyers receive for their speaking performances. Trial lawyers whose writings are barely intelligible usually speak persuasively. Lawyers conclude speaking is more important than writing, a conclusion the lawyer's distribution of time confirms. Lawyers usually spend more time speaking and listening than writing and reading, and aspirants consider law a speaking profession.
Writers' and speakers' talents overlap, but interests and inclinations that favor each differ; for one thing, writing is solitary, speaking, social. Lawyers are mostly oral beings. I prefer e-mail, but I make a phone number available for lawyers, whose comfort with telephony attaches distrust to outcomes otherwise arising. The conflicting imperatives for speakers compared with writers and the attractiveness of law practice to the speech-oriented best explain why lawyers often write badly.