Unclaimed doesn't mean it hasn't been sold already or that it has even been distributed to a retail location. Someone could hold onto a top prize ticket until the last day to claim.
Some have theorized that states control the top prize tickets and may end the game before their distribution or place them in places that sell very few tickets to avoid them having to be paid out.
There was a case in Indiana where a store was going to lose their lottery license. The lottery knew it was upcoming. One one of the last packs they received on a $20 game was a top prize ticket. Well someone with the store scratched off all the tickets in the pack and found it. Due to the fact that their license expired and the pack was distributed to them, they could not activate the pack and were required to return it to the lottery per the terms. Well the people involved with the store were able to get the stores lottery account reactivated to activate the pack and claim the prize. After spending a lot of the money they were arrested and charged with felonies for fraud.
The question is, in that case, did the lottery knowingly send that top prize to a store who's license they knew was ending and the pack would then be required to be returned to the lottery and maybe destroyed, saving the lottery a $4 mil. payout.
If you look at it this way. Here, the odds are calculated on a total number of projected tickets for a game, let's say 2 million tickets. As a player you would want the top prize tickets to be randomly distributed. As in, the lottery doesn't know where they're at and doesn't decide when and which retailers their distributed to. That way there wouldn't be other factors involved as to when/where the tickets are sold other than from the random mix. The issues for the lotteries is that people are less likely to play if they know there are no top prizes remaining.