I think it's good because of the large difference in material and space imbalance. White isn't just up a minor piece, this is a Q vs R position where white already holds much more space than black. When white is up material and black effectively has no pawns off the starting line, there's not much white can improve other than it's own king activity/placement. Kh2 is the natural attacking progression that is also the best 'waiting for black to make a wrong move' move if that makes sense. Hope this helped clarify. (FTR I probably wouldn't have found Kh2 despite now seeing why it's certainly best)