im trying to look for information y Arriva North east pulled so many services out of Sunderland so many year's ago?

We had the likes of
213 Darlington - Sunderland;
215 Bishop Auckland - Sunderland;
216 Thornley - Sunderland;
217 Bishop Auckland - Sunderland;
230 Hartlepool - Sunderland

There's a list of changes Under Peterlee changes in 2008 on the bygone era but it just says renumbered for most services but no reason y some were some were withdrawn.. was this due to GNE dominating?
With it being a Sunderland company i would of liked it to be the main operator in the city.