The one-sheet-of-paper requirement dates back to the early 1980’s. At that time everything was kept on paper, not in computer files. Ken Young kept the list at that time, and put out an annual printed book of certified courses. It was about a half-inch thick, and each course listed took two lines.
When I began keeping the list I noted that numbers were increasing, and I looked for a way to keep the size of the book to a minimum. By condensing the course number, and substituting “drop” and “separation” for the previous “start-finish-high-low” elevations I was able to shrink the data so it all fit on one line.
It has remained that way since, even though we now have computers to do the heavy lifting.
One good reason to have the course map on one piece of paper is that one document defines what is certified, not two or three. It is usually not hard to get the course map to contain start, finish, and TA locations all on one sheet. A list of splits can be on another piece of paper.
In fact, no listing of splits is required at all, if those splits are not measured or certified. Most people include them though.