Man, as an external observer I skimmed through most of hololive EN's stuff and I can see why a lot more people flock to Gura
Obviously we're discounting JP, sorry to those who like them, but they're literally swamped by the language barrier.
All the ENs in my opinion have their niches but it is Gura who provides that sort of general entertainment that's literally all you need to succeed in youtube.
Mori is weird. She comes off as some sort of "cringe" weaboo who nonetheless insists on wearing a cosplay. But she's got her songs so it makes sense that she's second highest.
Kiara is a sort of an odd one. Her accent really puts off a native speaker like me, and she collabs a lot with JP, which again puts most casuals off. And like Mori she has again this sort of "cringe" Japanese idol type of energy that really doesn't mesh well with your casual watcher. It's like that kid shouting "I've got anime on my side" except unironically (though I know its just part of the character)
Ina'nis is really one that settles into her niche. I can almost describe it as a much more restrained, relaxing type of streamer you can also find sometimes on twitch (mostly speedrunners). And of course, she is a proven artist of some caliber, which yet again adds to her niche.
Now Amelia is the gamer, and seems to be closest to Gura in terms of general appeal. It sort of makes sense that they get paired often, they really gel well in terms of personality. I am rather surprised she isn't higher, so there might be some factor I'm missing. But I guess going full into the image of a gamer girl does not really make you stand out, because there are already plenty of other choices for that. If all you're offering is being a variety gaming streamer, then some won't see the appeal other than "anime girl".
Gura just has the full package. She can sing, she can play games--not well, but at least she has her specialties--she has an easygoing personality that doesn't immediately trip the average "cringe" sensor like the first two, and just like old cartoons, she can be racy without being outright explicit. If there are children watching her for being a cute shark playing Minecraft, her jokes will fly well above most of their heads.
I'm not a fan of any of the five, but I can certainly see how Gura pulls in her fans. And it's worth stating that vtubing is still a relatively small and niche thing, which makes her more of a big fish in a small pond. There are literal giants of entertainment in youtube with more pull and influence on the greater social sphere, and that's not even getting into actual stardom. (Admittedly, vtubing also fulfills a demand that those aforementioned talents cannot provide but thats another topic)
