Most likely that the Thomson aircraft & crew combination were not certified for the approach required and the following aircraft was. There may also me differences in minima, which allowed the following aircraft to land.
It's not a conspiracy. It's not operationally easier to have aircraft on one side of the Pennines and passengers on the other. It's costly for the airline, to shuffle aircraft, passengers and crew around. The captain made a call that he/she couldn't safely get into LBA on that occasion, or was limited by minima. It happens at every airport, everywhere. The only airline that never diverted is the airline that never flew.