BMI's problem may be the number of new(ish) options available from the West of Ireland to Scotland. Check out the following - apart from NOC - GLA with BMI there's
SNN - PIK with FR
SNN - GLA via BHX with BE
SNN - EDI via BHX with BE
GWY - EDI with RE
GWY - GLA with BA (Loganair)
CFN - PIK with RE
I know most of these are on smaller planes (RE ATRs, BE 146s) but I cannot see enough PAX to make all of these pay - hence BMIs problem. Then again FR pulled a flight at short notice from a european route from SNN (I think it was CRL) when they launched SNN - PIK so maybe someone believes theres money to be made there.