In the first years of DVC, owners booked their home resort at 11 months out from their check out day. To make sure they got their stay, owners would book single night stays starting on the first day after check in (11 months out). They would need to call to do this because there wasn't any online reservation system. They would tell MS each morning they called that they were adding to their first night (continuing reservation) until they got all of their nights. No one could book a night before them unless they talked to MS right before them on the same morning. The number of people booking was limited to the number of MS staff monitoring phone calls. For popular times, you might be waiting to make your reservation until another CM became available.
Then about 2005 or so (not real sure on the exact date), DVC allowed members to book their stay based on check in day for up to seven nights (eight days). In this case, if someone called the morning before you because they were checking in the day before you, they might have booked the last studio in the same resort you were planning on booking for a seven night stay. Plus with on line booking, many members could be booking their stay at the same time at 8AM ET until the computer system was maxed out.
In addition, people have gotten saavy about renting points at 11 months out to get those studios for the cheapest deluxe stay they can get. That, too, might change with the issues arising with the resorts being shut down during the COVID-19 period and people avoid problems by not renting points.