Honestly, I think now is probably the best time in history for discoverablity by far. Things like YouTube have done a lot, but I think Steam has played a massive part. Compare it to most of the other options:

Physical retailers tend to just be a wall of products, with the exception of games with a large marketing budget (esspecially those working out deals directly with the retailer) that often get special placement in their own shelf. Marketing budget is king, and everything else is hard to browse.

Reviewers offer a bit of an advantage as they provide an easy way to assess if games are good or bad, but they are usually limitted in the number of reviews they can publish, and those reviews tend to go towards the games that get sent from powerful publishers or those with most hype, meaning it usually still comes down to marketing budget.

A step up from that is most online retailers. Here, you have easier access to information about the games on display, and often have ways to sort by genre, price, or reviews. That said, a lot of emphasis is always placed on either the top grossing, games directly connected to the storefront owner, or games that directly buy space on the front page. This offers far more discoverability than anything that came before, but still tends to massively over-push higher-budget and/or higher-return games.

Steam on the other hand, has put far more emphasis on featuring good games on their front page. You can't buy the space, Valve doesn't bias the store towards their own products as much, and revenue plays a generally smaller part in the algorithm. Instead, they have a much better personalized recommendation algorithm and more tools for customizing your storefront (such as blocking tags). On top of this, they have recognized that this isn't enough, and introduced a myriad of (often half-baked) additional discovery tools, such the the Discovery Queue, Curators, and the various festivals like NextFest. Sure, its not perfect, but I can consistent find new games I'm interested in, whereas on other platforms its barely worth trying. I think this is a big part of Steam's success that often gets overlooked.