It's a massive waste of money.
They want extra London services from Bradford purely to appropriate more of the fare box. It's called revenue abstraction.
It will reduce Northerns "share" of revenue from the Bradford to Leeds flow.
Long term, this will mean more subsidy for Northern is required, and potentially service cuts for local stopping services.
It's what they already do on the Harrogate line, when they can be bothered to actually run the trains.
On the Harrogate line it's a better and more reliable service when LNER cancel everything as their presence causes constant delays and congestion.
I would be overly optimistic if I did not expect the same to occur when the London element of services from Bradford foster Square is ramped up.
As was mentioned by the OP, there are far better things to spend money on.
But Northern and LNER (also now TPE) are both wholly owned by DOHL “nationalised” and so one cannot abstract revenue from the other. If any combination of Northern, TPE and LNER run on a route, then DOHL in one form or another receives 100% of the revenue. The branding is irrelevant. It simply becomes a choice whether to prioritise local or intercity services. This is not like talking about private TOCs.
My understanding is that in an ideal world, the connections from e.g. Harrogate and Bradford to Kings Cross would be so high quality that there would be no question of direct services being unnecessary.
However we are where we are and we are left with a paradox. In reality, these connections are SO unbearably unreliable, especially for infrequent travellers and passengers unfamiliar with or otherwise restricted in their ability to use the railway, who cannot be feasibly left with long waits at a large, crowded station that they are not comfortable to remain in, as opposed to a train.
The connections at Leeds are unreliable because of a lack of spare capacity, particularly at Leeds station, so the solution, for passengers outside Leeds with direct services to Kings Cross, is for these services to consume more capacity by reversing at Leeds with a long dwell and continuing off-pattern to other destinations, compared with terminating intercity services at Leeds.
This guarantees passengers will enjoy a comfortable journey to Wakefield and Doncaster in addition to Kings Cross, without inconveniencing passengers originating from Leeds, but is somewhat self defeating in its aims. Regardless it remains the best option currently and until there can be a doubling of or greater increase in capacity at Leeds station (HS2 anyone) which itself will release spare capacity for more of exactly these same through services.
