>>3008195Fubuki was one of the first and most succesful ones back then, and also was and still is considered to be the spokesperson of Hololive, so that's why she's one of the most subbed.
It's true her content is more mellow than that of others that came after her, but I'd guess this is also what people like about her. Mature may seem boring to those looking for more explosive stuff, but she's relaxing to listen to and quite interesting (providing you know japanese, although she has one very dedicated live translator). She may not be as funny as Pekora or Miko, but she's still capable of antics of her own. Not to mention her overall cuteness and radiance.
Personally, her hard work (representing hololive and helping other members, even male ones) and her very well-tuned moral compass is what made me love her the most. More than entertainment, she's an inspiration. Maybe that's how others see her, too.