Its the Matthew effect - Steam is going to show you popular games because they're popular, which leads to them being more popular. It's usually games with big marketing budgets/efforts outside of Steam that eventually hit 'popular' and then stay there.

If I had to contribute my extremely biased two cents: Steam recommends 'similar' games based on tags, popularity, and if your friends play it. You play Valheim, its going to show you survival crafting games, viking games, and maybe a third person action game. If another relatively popular game has all three, you're almost guaranteed to be shown it.

In the indie dev space you're trying to leverage this by changing your tags to a popular game similar to yours so players of popular game will hopefully get recommended your game. (Also a lot of devs do this which dilutes its potential)

My biased take is that these tags fall short and it leads to 'similar but different' game recommendations which eventually had your storefront dominated by mass sellers or the big titles in a specific genre trying to muscle in on the space that Steam believes must be your favorite genre(s) because you bought the games marked as similar that it recommended to you.

If you actively try to find niche titles via labs or whatever then you can get it better tuned, but for most people I think they usually end up seeing just already big and successful games.

Sorry for the long rant, thanks for coming to my TED talk.

CEO

TLDR: Valve ex employee makes up excuses about Steam discovery sucking. Main point being it's not Steam's job to make games discoverable, and that even if it were people only hear about new games on social media so it's pointless to try. Humble brags about trying. Post title is tangential at best.