It would be more fair to say that it's reasonably common that the US military routinely engages in humanitarian missions both overseas and domestically. I've been on one such mission overseas, but that was within the 20 year time limit.

Historically the US has deployed domestically during disasters, ranging from the linked mostly-engineering disasters to bad snowstorms to even use of naval vessels to provide electricity to the city of Tacoma.

Overseas the US military has deployed to help provide relief during major floods in the Netherlands in the 50s.

From a disease standpoint, the US Army did a sterling job of stamping out Yellow Fever at the turn of the last century, and the Walter Reed medical center in the DC Area is named after a American officer credited with the eradication scheme.

The reason why the military is ideal for use in disaster relief is because, frankly, there's a clear chain of command, are better equipped to move around when local infrastructure may not be reliable, the personnel follow different laws than civilian agencies(you can't just quit and flee the area if you're ordered to help someone), and honestly, there is a degree of physical deterrence involved in preventing people from getting out of hand.