Early Morning DUB/LHR.
I really doubt BMI are that naive . They have competed on shorthaul routes including Dublin for many years and I-m sure they know what they need to do pricewise to maintain a fair share of the traffic.
I suspect , until now the winter schedule has not been finalised .
They may not have known for definite if the early departure would operate and/or what equipment would be used ie. Airbus or RJ.
In such circumstances it doesn-t make sense to sell a lot of cheap seats early
and then find you only have 50 seats instead of 150 and no capacity left to sell to the late booking high yielding traffic.
BMI has previously had these sort of problems on UK domestic routes when last minute changes to schedules/aircraft type left them overbooked or at best nothing to sell.
It looks like they have been prudent in this instance and have waited until things are more definite before opening up capacity.
I know other airlines including BA have done this.
If they close the flights completely ,it starts hares running with Travel agents or travel press or Ppruners noticing the flights are closed out and the assumption is made the route or frequency is being pulled.
By closing down inventory to only Flexible Y fare , this deters the early booking bargain hunters .The late booking business travellers who will pay the high fares aren-t booking in this time frame so they aren-t affected.
Even the lower yielding traffic doesn-t book very early ( apart form peak dates like school half term and Christmas which will fill even if opened very late ) , so not a lot of this segment is lost.
I would say good Inventory Managemnet by BMI.