Too expensive more like.The CTC overheads are killing NSL
A comment presumably based on detailed knowledge of the costing of the NATS Gatwick bid or perhaps just an assumption on your part.
In this case you needed a certain amount of "overhead" to be invited to bid. If price were everything and capability beyond the immediate Tower operation wasn't required it would have been a very different short list. DFS is just as capable as NATS, in some areas more capable because it hasn't been subject to quite as much pressure on costs over the last 15 years.
We don't know the details of either bid and probably never will but it is always easier for the newcomer to bid low than it is for the incumbent. The newcomer can take a loss justified on the benefit of breaking into a new market and establishing a presence whereas taking a loss just to retain existing business is a very quick way of ending up with no business at all.