I think 2 issues at play;
- Its not a rehashed operation. This isnt a phoenix company from Stobart Air, they're setting up from scratch as far as their AOC, aircraft and staff are concerned. There will be a minimum lead time for that.
- IAG may prefer to use their own EI A320s and BA E190s for these fights at times of reduced demand, rather than bring in a third party which causes those aircraft to sit idle.