Your 7-month window starts on day x. That is not going to be a "common" starting day, it's just your closing day and anyone else that happen to close that day (in any year). If there are 600,000 members and closing dates are evenly spread between 365 days, that = 1685 members with a common closing date. Assume 1% of those want to go on vaction when you do, that's 16.85. Spread that among 8 resorts and only you and 1 other person want to go to the same resort as you do. True, some of these members will have your resort as their home resort and will have booked at the 11-month window. Some times of year are more popular and will have increased demand, but overall, most members get where they want, when they want. Accomodations are limited by resort, so a certain room type may be "tougher" to get.
Overall it is pretty simple. MS has to pick a date and it is the 11 month and 7 month booking windows. Pretty Simple. The day to day is not a recommended reservation method by DVC but a way that members have come up with to hedge their bet.