The size of the site does matter right now, since Steam is pretty dominant on the market and there isn't much reason for people to look elsewhere unless they're really interested in the indie game scene themselves.

I will say that a large issue is marketing as well. Most indie developers hope that getting on a front page or having a banner ad someplace will do wonders, and while it may help, there's a lot more that you can do. Look at the Big List of Youtubers, see who would be interested in your game, watch a video or two of theirs to be sure, and send them an email. It's exhausting (at least for me; I still need to finish going through the list), but contacting people for reviews helps out.

Twitter helps too; if you're an indie developer and not on there, seriously consider getting an account just because it's so simple to just throw hashtags onto posts with screenshots and store pages to boost your reach. I managed to get a couple very small channels to do a review on Youtube because I asked publicly on Twitter (and they were even pretty positive, like this one!). Even if the reviewer has no subscribers, don't underestimate the value of someone being able to type in the name of your game and be able to see someone else play and examine it.

Also, pitch your game at the drop of a hat. If a stranger comments on your shirt because they recognize and like the band on it, mention how you like whatever style of music it is, but that you haven't had much time to listen to them since you've been working on your game. Learn how to segway discussions with potential players toward your game and what makes it so interesting. Always have pen and paper on hand to give your game's url to people. It may seem insignificant, but I've made more than one sale and several downloads this way.

I'm sure there's a couple more factors as to why it's hard to find success on here, but I think the site size (and relative obscurity in comparison to places like Steam and GOG) and the average indie dev's marketing strategy to be the main issues.

most of my sales come from twitter. don't launch a game on the weekend. early in the week is good. i have a list of press people i send free copies of stuff to, and i send them at least a week before the game's release date, so they have time to write something. be really clear about basic stuff about the game in that email, like when it'll come out, how much it'll cost, and what URL they should link if they write about it (itch is cool cus you can set up your game's page / url ahead of time, then set it in preview mode to show to press). again, don't send out those emails on the weekend. i've heard tuesday is a good day, because folks tend to spend mondays catching up on stuff from the over the weekend.

i have always sucked at marketing though so no promises.

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.