Does anyone know why dwarves are doing so well?
They have quite a bit going for them...way more than most other species.
History: they are one of the more iconic races in the D&D game. They are present all the way back in the very first edition of D&D, and have had a strong presence in every edition of the game since. Across the different editions, they have remained one of the most consistent options for character builds, with the same straightforward role, history, lore, and abilities. When you say "I'll play a dwarf," everyone at the table can instantly relate to your character: you're the melee fighter in heavy armor, with a big hammer or axe, and a fondness for ale. (I'm not saying this is good or bad, I'm just saying that it happens.) This ubiquity means that they are easy to imagine in nearly every game setting, from ancient Egypt to Forgotten Realms to Spelljammer. Other species strain and stretch to fit in; dwarves just...do.
Pop Culture: that classic D&D dwarf has always been popular in media, especially video games and movies.
Deep Rock Galactic, Dragon Age, God of War, tons of games have the Tolkien-esque D&D dwarf idiom. Movies and television series like
Lord of the Rings, The Witcher, and
Game of Thrones have put forth more complex and "serious" roles for dwarf characters, helping folks reimagine them as more than just "beard with an axe." In recent years, "DwarfCore" music has even made it onto the music scene as well thanks to bands like Wind Rose and Clamavi De Profundis, which draw inspiration from the music of the
Lord of the Rings movies and the lyrics from Tolkien's work.
Also, John Rhys Davis.
Game Mechanics: in 5th Edition in particular, the Mountain Dwarf is the only species that gets two +2 ASIs...and they are in both Strength and Constitution, which are the most critical ability scores for characters that focus on melee combat (especially the barbarian and the fighter). The Hill Dwarf doesn't get the bonus to Strength, but instead gets extra hit points...combine that with the +2 Constitution ASI that all dwarves get, and you have a reliable tank (and if your DM uses feats, you can grab Toughness at 4th level for
even more hit points.) Duergar get a bonus to Strength, and they gain innate magical abilities that let them change their size and turn invisible.
I really don't think they will win (tall poppies and all that), but I would understand if they did.