Unfortunately in this day and age, it's actually cheaper for the airline to make (what seems) illogical decisions but let's weigh it up.
Option 1 - the situation you faced
2 coaches at say £300 each = £600
Cost of ferrying the aircraft = say £10,000
TOTAL = £10,600
Option 2 - the situation Thomson could have faced if the delay exceeded 3 hours
220ish people on a 757 meaning:
220 x £460 compensation = £101,200
If the BHX crew had gone out of hours this would have certainly meant that the passengers probably would have been sent back to the hotel, meaning you can add hotel, food and transfer costs to option 2...