Wait two more weeks and then go for it. Note that the 499 day limit is based on your check-out (and not check-in) date.
1) For really busy times (Christmas, Halloween), in many cases, people book day-by-day.
2) They "link" the ressie so they can stay on the same site, which usually works.
3) If folks waited until their check-out day to book the entire stay, others might have already taken enough single days to fully sell-out the resort, or at least a category.
4) The Fort has become so popular that it is now one of the most desired, and sought after, resorts.
. . . more older folks are buying RV's
. . . with financing, even younger families are finding the enjoyment in camping
5) The experience at The Fort is unlike other Disney resorts
. . . people actually talk to one another, even when passing on sidewalks
. . . campers are a unique breed and tend to socialize with total strangers, let alone those they see year-after-year
. . . there are so many activities at The Fort, that going to the parks is not mandatory
. . . campers usually take things at a leisurely pace, instead of the "commando mode" touring schedules of other guests
6) All these things make ressie hard to get in Prime Times.