Spreading responsibilities , costs and blaming the others
The UN has enormous advantages:
You can blame IT rather than yourself when your own troops are there and can't see much progress.
You can ask other countries to send troops and do the ugly job in your place (they'll pay for it and that's less money from US taxpayers).
UN troops don't have political agendas where they are.
But the UN has never a mandate to attack minorities for the sake of attacking (or displacing people); but it gets mandates to protect groups from each other.