Why is Unionism not interested in nationalists?

This the first of two pieces I’d like to post back to back. Tommy McKearney argues that Unionism shows not the slightest interest in attracting Nationalists to its cause and is therefore doomed to a long term and possibly terminal decline:

After years of insurrection, you might imagine that even the dimmest unionist would understand that the very existence of Northern Ireland is threatened by nationalist/republican alienation. Surely enlightened self-interest would dictate to them that every effort should be made to encourage nationalist/republican co-operation within the state they have long mistrusted.

Clearly hinting at the troubles in North Antrim he concludes this point:

Yet, like the alcoholic who resumes boozing after his liver transplant, unionism is determined to remain embedded within its old and for it, counter-productive habits.