Buzzfeed does a lot of fluff ("You won't believe these 87 talking cats") plus decent, fairly well-regarded journalism (paid for by the fluff). This actually isn't that different to how normal papers operate; sports, gossip (called 'society' if the paper is sufficiently fancy) etc, bring in the money, with investigative journalism not exactly being a big earner. The difference is that Buzzfeed had the fluff before it did journalism.
Due to the travails of the news industry, there are currently a lot of good journalists and not a lot of jobs for them, so this sort of non-traditional route works. Teen Vogue is another example, arguably, though a less dramatic one; surprisingly good journalism in an outlet where you wouldn't traditionally expect journalism at all.
Buzzfeed News has a lot of excellent journalism. Even in its non US editions, like India for example. They cover a lot of important stories that the mainstream outlets refuse to touch.
Like other comments have already mentioned Buzzfeed (not Buzzfeed News) is the low effort listicle / clickbait part of the business which is unfortunately better known (mostly for pioneering the entire "10 things... you won't believe number 7" genre)
