One important reason is that a chief sustainer of any state is the myth of invincibility. Once the cracks start to show, as Gorbachev discovered when he lost his job and the Soviet Union, the whole shebang can quickly crumble. When India was struggling for independence they looked to the lessons learned by Irish nationalists. This is not to say that a British withdrawal would spark revolution throughout Britain, but certainly it is a risk for the British government to allow such an upheaval, a risk that for the moment they are not willing to take. At the moment though Protestants still are marginally better off than Catholics.
Unemployment is two and a half times higher in Catholic areas.
However, loyalists believe that talks such as the Brooke talks could be a forum for Britain to slowly slip out of the North. It is to prevent this happening that the 'orange card' is again being played. It is for this reason loyalist sectarian attacks occur, they serve to divide Catholic and Protestant and ensure thus that the Protestant working class will fight to maintain the status quo i.e. its allegiance with the bosses and the state. This isn't always the case though. There have been times when both sides united, for example, the DHSS strike against UDA death threats to Catholic workers.