Aer Lingus are steadily growing transatlantic capacity, with the addition of new aircraft this year and then again in 2018 with 350's, it also has significant work with ASL. In percentage terms the T/A business is growing strongly and is being developed with prudence.
IAG is a commercial enterprise, and I would guess that there is competition on a commercial basis for the capital investments that they make. IB are getting new units for their lucrative South American routes etc.
Willie Walsh has went on the record in relation to the possibilities of getting second hand aircraft which may come available, I realise this was more for short haul, but if such aircraft can be secured, the lead time may not be as long as say buying new from Airbus....or indeed Boeing.