Perhaps a better question is “why does the award of humanitarian of the year exist?” I assume the answer is to raise awareness of charities and the issues they are addressing. If the point of this award is to raise awareness (and possibly use that to raise funding or apply political pressure to tackle the issues), then Harry and Meghan are the perfect choice, they will turn up for the ceremony and have their photos taken. Newspapers and tv news/gossip will show the photos /footage (in a way they wouldn’t for other winners) and talk about why they’ve won.
I know people on here are increasingly frustrated H&M haven’t sunk into obscurity, but any story involving them does still grab the public interest so cynically they are always a good choice for these things.