It is understandable that readability is not a major concern. Regulatory writing is generally considered the most rigid and standardized genre of medical writing. The industry around the world follows ICH guidelines and templates for study reports, protocols, and summaries, which can breed a sense of complacency. Regulatory agencies employ experts in the review of applications, who surely do not mind highly complex data presentation, dense text, and lots of jargon. In addition, standardization and uniformity are indeed important in technical writing (that's another subject onto itself), although they are often confused with a lack of flexibility. Most important, submissions are often put together under very tight deadlines, and there is simply no time to bother with such "luxury" as document readability.
So why does readability matter? The answer is simple. On the other side of each submission, a real person will read these documents, and it is to your advantage to get on their good side.
When I worked as an FDA labeling reviewer, I read many briefing packages and new drug applications and, in some cases, felt the frustration of wading through poorly written and illogically organized text. I heard medical reviewers sigh with resignation. One person said she wished that poor writing were grounds enough for refusal to file. Poorly written documents take longer to read and absorb, are less persuasive, and reduce the effectiveness of the message.
Think about the workload of the medical reviewers who will look at your submission, and imagine how much a crystal clear, easy-to-read, logically organized application would lighten their mental load. Everyone has experienced the sensation of smooth sailing when reading a well written article with no "bump" of confusion or disconnected reasoning. The mood of the reviewer depends on the readability of your documents, which in turn may leave a general impression in your favor. Even if your data are overwhelmingly and indisputably positive, readability can substantially reduce the review duration and get your product on the market a few days before the mandatory review deadline. This can mean thousands or millions of dollars in extra revenue or an edge over your competitors.
Nathaniel Hawthorne wrote, "Easy reading is damn hard writing." That truth applies even more to technical writing than to fiction, where data are abundant and complex.