I have a tiny YouTube-channel where I make Videos about recently released Indie Games in German. For me one the main reasons why I decide to cover a game is whether or not I've heard of it, or its developer before. The game may not get released on Steam, but if your name rings a bell, I'm probably going to cover it. I have weeks where I get drowned in emails and even though I don't like sorting stuff out, I kind of have to in order to get things done. Knowing the name of a developer is one thing that really helps in that regard.
One thing that also helps are follow-up emails. I sometimes forget about games I actually wanted to cover and ended up covering them, because a developer reminded me of it. Sometimes I also don't have the time initially to cover a game, but I might have it by the time I got reminded.
To be honest, I think the impact YouTube has on smaller games is a bit overestimated. Sure, it could boost your game's visibility by a lot, but it's still incredibly tough to get to the point where channels want to cover your game. Most of the time, it's not those larger channels that "discover" a game, but it's smaller channels/sites that specialize in these kinds of things.
I think it's a similar kind of survivorship bias you see with succesful indie devs in general. Since you only get to hear the stories where getting coverage from a large YouTuber saved a developer's business, you tend to think that it happens to everyone who does get covered by those people. That doesn't mean that you shouldn't try to get coverage from those channels. However I think it's much more important to get to a point where people start talking about your games on a regular basis and not only after you released your game.