Did MON not increase their fleet size a couple of years back to increase economies of scale? What's changed now to make fewer aircraft the way forward?
Looking at it from the outside it's hard to see a market for them though. EZY/FR have the low cost market sown up. Jet2 are dominant in the north with a package holiday/low cost airline combi, TOM/TCX have a large presence in the charter business. At some of their main bases, MON face huge competition:
EZY/Norweigian/BA from LGW
EZY from LTN
EZY/Jet2 from MAN
Jet2 from LBA (if they stay there)
Only BHX offers some sort of chance, with no low cost carrier based there (yet). It's hard to see a clear differentiation and while most people would probably instinctively prefer to travel MON v EZY/FR, the actual product isn't any better and doesn't justify higher prices.
Good luck to everyone involved with the company