Trump loses interest in the more pressing matters of helping devasted Puerto Rico and the presently being devastated wildfire areas of Northern California because literally Trump is the kind of person who quickly loses interest in anyone whom he perceives as wanting something from him. It is a rich guy thing.
Instead Trump embraces the sense of power and is attracted to the historical presence that surrounds a president or leader involved in a conflict of nations. Helping millions needing food and water in your own country is boring like a teenager having to do a household chore whereas playing Chickee with North Korea and contemplating the use of force such as only America can wield is almost intoxicating!
Trump simply cannot hold his attention on things like helping others. He loses interest that kind of thing real fast!