That firehose isn't pointed at everyone, being the newest game on Steam has a very fleeting value and then it's on you to find customers. It used to be that Steam played a much more active role in spreading traffic around games but these days the median game is doing $1,000 - $2,000 in sales which is like 100 - 200 copies sold. It's more and more like Google and Apple where what you get out of it is just a function of how much you spend on customer acquisition, how well you reach social media, and whether you can leverage these to become popular enough to achieve prominence.

Everyone launches on Steam because they are an utterly-entrenched monopoly, all other PC game distribution channels are collectively a very small percent.