Perrin
Its a good question "why do Ryanair seem to cancel first" i can only assume that they make more or lose less by bunching people on to subsequent flights? plus many will simply not bother to reclaim their money and a lot of tickets will have been sold at below cost in what is a shoulder period, for sure you can bet they wont have done it to increase their costs.
If you had two aircraft flying with say a 130 paxs and half were on "sale" tickets you could probably improve the yield by flying the next day with one full aircraft.