The problem is, is that you have folks like us who make the reservations far out in advance to ensure we get them, but with the mind set that it can change. (Although for us it usually only changes to "Extend" and not shorten).
Then the folks who wait, what might otherwise be a reasonable amount of time in advance, go to make their reservations, but can't quite get the dates they want, so they take alternate dates. Then... plans change as the date gets closer and people modify their previous reservations. That means maybe the date you wanted opened up, so you change your reservations, which then allowed someone else to get the dates they wanted (your old reservations), etc... etc.... etc.... and on and on.
So for us we try to solidify our dates well in advance so that we can reserve our dates and lock them in. I still think it's better then taking the chance of waiting and end up taking something other than what you really wanted because that was all that was available.