Jet2 only allow tour operator allocations to the canaries when the flights are operated by 757's. Selling seats direct to Jet2/Jet2Holidays customers has much higher margins than tour operator allocations so selling 50 seats to Thomas Cook means that only 98 seats are left to actually make a significant profit (based on a 737-300) conpared to 180 seats on a 757. You might find that Thomas Cook will not be taking allocations on the Jet2 Tenerife/Lanzarote routes over January/early feb as it is mainly operated by 737's over that period.