My way of explaining what PPs already said:
Let's say I have a popular home resort.
At 11 months, only owners who have it as their home resort can book there.
At 7 months, any owner can book there.
That means that getting a reservation there between 7 months and 11 months is easier than after 7 months, because fewer people are allowed to book there during that time period.
If you really want to stay there, you are more likely to get a reservation if you tell the agency early enough so that the agency can have an owner book it for you between 7 months and 11 months. If you wait until after 7 months, your dates might be sold out.
So my points between 7 months and 11 months are a more valuable commodity than my points after 7 months.