I think that’s generally because somebody influential will kind of take the game under their wing. Pewdiepie did this, once. I can’t find the Kotaku article now, because it’s buried under dozens of articles of Pewdiepie controversy, but it was this super unknown indie game, sold less than 250 copies, and Pewdiepie did a single video about it and I think the developer said he never has to work a day in his life ever again.
Obviously that’s a large scale example, but there are smaller scale examples where people with audiences in the thousands or even the hundreds are trusted and can spark word-of-mouth buzz.
But you have to be able to find games to begin with. I’m one of those guys who will go digging for this stuff – I loved sifting through Xbox Indie games back in the day, for example, and seeing all of the weird stuff that came out of that, like Escape Goat and Apple Jack and Cthulhu Saves The World. But I find Steam to be completely exhausting in that regard. The signal to noise ratio favors noise more than anywhere else I’ve seen outside of maybe like, the Google Play store or something.