The trick is to sell tickets based on the cost at time of sale, and just cancel flights when it's convenient.

When airlines cancel flights, they usually put you on a similar itinerary, not just refund your money and hope you rebook at a higher price.

That said, I don't know a lot of people that book that far in advance, even when their travel plans are well settled.

It doesn’t work that way. Canceling flights has significant business-impacting downstream effects that go beyond mitigating the loss caused by a bad bet.