Basically, with every visibility rung your game climbs, Steam gives you a bit more visibility, and if your game keeps performing well they show you in more places.
I explained it in depth in this lecture, but Steam visibility works like a ladder. Basically, with every visibility rung your game climbs, Steam gives you a bit more visibility, and if your game keeps performing well they show you in more places. Eventually with enough visibility you will get 1000 reviews.