It seems a fair few flights have been cancelled and delayed today at Amsterdam Schiphol not just Durham Tees Valley.
It seems that Durham Tees Valley is one of the first routes to be affected when flights get cancelled due to weather / reduced landing slots at Amsterdam Schiphol.
I suspect it's because KLM know they have no competition to worry about at Durham Tees Valley so make the decision to cancel that ahead others routes which they have a chance of losing costumers to other airlines / routes.
I guess they also have to factor in the size of the aircraft, what the load was for the flights, onward connections passengers, how passengers can be accommodated on alternative flights / including use of other local airports with KLM flights to Amsterdam Schiphol, cost of cancelling flight i.e. compensation etc, airport landing fees and charges.
i.e. KLM decide to cancel a Durham Tees Valley flight. They contact passengers and offer alternatives of compensation / costs plus a seat from / too Durham Tees Valley Airport on earlier or later flight or seats on flights from / too Newcastle airport or Leeds Bradford airport.
KLM won't cancel the route because it makes them a lot of money. If routes like Durham Tees Valley were cancelled it would have a negative affect on other flights / routes from Amsterdam Schiphol because most of the passengers are connection passenger and most will be going onto another KLM ticket coded flight.