People don't play Dwarves because in most media, Dwarves are depicted as jokes or punch lines, always secondary to elves and humans, or humans and orcs, or humans and other humans. People don't like to play short hairy guys who get made fun off, a lot of their player base role play as that in real life anyway lol so I don't see it as surprising.
As for white, 90% of their player base are American or European white men, people play characters that reflect or look like them, despite what people insist, fantasy is about going to a fantasy world, it is not about being a fantasy being, people create things they can relate to, white men can't relate to black Dwarf women. Women play female characters most of the time.
And for the priest and people's obsessions with assassins and doing damage with fighters, people play these games to go on adventures, they don't play them to support other characters having all the fun, healing and buffing isn't heroic, it isn't what people think of when you think fantasy, they want to be the powerful wizard or the mighty warrior, or the cool assassin, they don't want to hide behind their party healing them or making them do more damage.
tldr; people want power fantasies that are relatable to them.