According to information already posted either in this thread, or in other places.
Manx2 does not have an AOC, they use the AOC of the operating company, so in this case, the AOC is Spanish.
Manx2 is only a ticketing operation, and as such, they then contract, under quite strong contracts, with the aircraft operator.
The following is RUMOUR.
The fuel on board was possibly trip fuel only, as Jet A1 is apparently cheaper in Cork than in Belfast, and a LOT cheaper that fuel for internal flights.
The captain was a very recent command appointment, so depending on the SOP of the operator, he may not have flown many ILS approaches to landing.
The FO was a recent appointment, and it is unlikely that he had flown many flights on Metro.
The operator faces severe financial penalties from Manx2 in the event of delays or diversions.
At the scheduled time of arrival, the primary alternate was also below limits.
The possible alternates of Kerry and Waterford were probably not available to the operator for lack of handling agreements and agents. That would have left Dublin ( not a Manx2 destination) or Galway, both significant distances from Cork.
For me, that's more than enough Swiss Cheese holes for a lifetime, and the thought of adding any of the many possible additional items mentioned above is beyond scary.