This may take a while to explain, so bear with me -
The inventory of rooms available for cash is completely separate from the inventory available for points.
Points inventory comes solely from the members' ownership interest in the resort. Cash inventory comes from several places.
Disney maintains about a 4% interest in every
DVC resort. Those rooms are available to be rented to the general public for cash. Disney gets the money. Any unsold potion of a DVC resort (aka Developer's inventory) is also available to be rented for cash. Again, the money for those goes to the developer. The largest share of the rooms available to be rented for cash are the result of members choosing to use their points for non-DVC options -i.e., non-DVC WDW resort stays, cruises on
DCL, and/or choices from the Adventurer's or Conceirge Collection. When that happens, DVC "transfers" the equivalent number of DVC resort room nights into the cash inventory. The money from those rentals goes to pay for the non-DVC options that the members wanted to experience.
Also, points inventory that is unreserved by members at the 60 day mark is made available for cash rental. Money from that goes back to DVC and is used to offset dues (called breakage). Members can still reserve rooms with points during that time, but are competing with those wishing to reserve for cash. Of course, both points and cash rentals are subject to availability.
As far as when the public can make a cash reservation, it just depends on availabiliy of rooms in the cash inventory. There usually isn't all that much available a long way in advance. As members use their points for other options, more becomes available.
HTH.