I vaguely remember when the new Teesside Airport halt was constructed and opened at public expense, and was served by a United single decker bus connecting to the terminal.
I also remember travelling many times on the train between Darlo and Yarm, and stopping at Teesside Airport where nobody got on or off, and said bus sat there forlornly empty.
Then the bus got binned, and the alternative of Dinsdale was tried as a sop to objectors. The privatised rail company took the view that there was no point inconveniencing all the users of the train who didn't want to go to Teesside Airport having their daily commutes interrupted by 2 or 3 minutes each way while the train pointlessly stopped there. The direct bus service from Darlo station (much faster than changing trains at Darlo for MME station plus the bus link) also failed.
The station with direct terminal bus-link failed when pax numbers were much higher and there was less access to car ownership. Why on earth would it make any difference today, with lower pax numbers, greater car ownership (and the airport having an underutilised car park) ?
And let's face it, the rail route between Darlo and Teesside conurbation is hardly an example of modern high-speed frequent inter-urban travel. It would take a damn sight more investment than just a revamped Durham Tees Valley Airport station to upgrade the entire travel experience as a genuine alternative that compares with NCL's metro service, BHX International, MAN airport, and etc stations. And for how many potential passengers per day ? There are far more deserving public transport projects in the NE looking for funding.