6 flights a day sounds like 3 aircraft stood down. There is capacity available from other operators in various countries, but presumably not at a price TUI's board are prepared to pay. Yes, they will lose money. Yes, some ACMI owner will be able to buy their second yacht on the strength of it. But you have sold your product and now have to honour your commitments. All a bit surprising given that even in the IT world a good 10-15% of business typically comes in the last few weeks before departure.
Harry Goodman at Intasun used to do this, wait until others had firmed up contracts and then come in and offer the airlines and hotels less to pick up the remaining capacity. Somehow he always managed to get away with it, the failure of Air Europe was due to other reasons.