That may be accurate for commercial contracts but lawyers write lots of other documents too, some of which are subject to thousands of edits. Think about judicial opinions, advices, written arguments, continuously updated legal commentary services, public reports, or indeed statutes. These documents are often carefully drafted over months and complex manual protocols get set up to manage it, due to the limitations of Track Changes and the lack of familiarity with the tools used by software engineers.
Legal agreements are basically a war over each party's choice of standardized language followed by battles over customized terms.