I would imagine that the 195s have been chosen to operate on busier unnelectrified railway lines where their excellent acceleration and deceleration is of good use, particularly the routes around Sheffield which are resourced from Neville Hill. By comparison most Heaton worked routes do not interact with other express passenger services.
Imagine it'll be political aswell, it won't look good for the North East if all they get is, at best, cast-off 15 year old trains and everywhere else is getting shiny new trains. I'm sure the two Mayors in the area would have something to say about it aswell.
When even was the last new train up here, a Pacer? Because I'm struggling after.