Because of self-determination. It's up to the people of Northern Ireland. End of.

Northern Ireland could very much hold a vote on independence if its devolved government ran on a policy and got a mandate on a vote for independence, and reached an agreement with the central UK government on it.

It should also be pointed out that not even the Republic of Ireland would want to absorb Northern Ireland at this stage due to cost and political instability.

Northern Ireland is heavily subsidised by the rest of the UK, a cost which ROI cannot afford.

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