Because of their 50+1 strategy, they have made zero meaningful attempts to reconcile with unionists, because they feel that by fucking their way to a UI, they don't have to even try. You should have a look at social media for the threats to unionists by nationalists. We'd be storing up a barrel of shite by having anything to do with them.
It's a case of 50+1 and if you don't like it, you can go or be forced back to the "mainland". There were 18 peace walls back in 1998, now there are in the region of 60, totalling over 34kms.
And in education, 93% of children are segregated.