Ddolbang's art isn't particularly great (I find the style kind of safe and bland personally), but it's functional, which is why it's become so prolific. Because the style's so simple and easy to replicate he's able to put out art of every expression you could possibly need for every vtuber who catches his interest, and because they're transparent .pngs they're more flexible for thumbnails etc. than full art with busier compositions.
It feels cynical to draw for function rather than for art in a fan space like this, and this mindset taken to the extreme is what makes Calarts slop look so hideous, but at the same time I can't really knock him too much for finding a consistent gig and keeping at it.