In my experience, the 6:00 outbound and 21:30 inbound KLM flights are pretty full, 80% of who are business people linked to businesses in the Teesside area. Whilst there is not a great deal of tourism business on the AMS route and overall passenger numbers are not huge, the route supports a wide range of businesses (and therefore jobs) in the Teesside area.
Business people want convenience and are less price sensitive than people paying their own fares. The problem in our area is that there are not enough of them to warrant more routes and higher usage of the airport.
Of course Peel are sat on a huge land asset but for the moment they seem content to lose money on the airport whilst slowly exploiting the land. As far as KLM goes, judging by the pricing on various routes starting at MME I suspect they are quite happy with the money they are making here.