TC probably haven't actually sold them yet but are waiting on the possibility of last-minute package bookings. It'll be no good to them if they've got rooms available and no seats on flights.
Do you really want him hanging about at DLM for, possibly, days on the off chance of getting a flight ?
You'll more than halve the price by going with scheduled airlines and being prepared for more than 1 change. Look for instance at DLM - IST - AMS (Amsterdam) - LHR/MAN or DLM - IST - FRA (Frankfurt) - LHR/MAN