Why would you skip important meetings at the UN to go on campaign trips if you are so far ahead?
That one is too easy. Campaigning to the tune of mindless obots is easy and does wonders for his ego.
Going to the UN isn’t easy.
He has to share the limelight
He might be embarrassed if someone asks a question without a teleprompter. Very hard to hide one in a coffee table visit with other heads of state and there isn’t usually a script.
He can’t do anything constructive for the good of the country.