Yes of course you have to market outside of Steam. But actually most traffic to the game page will come from people discovering it through Steam. Especially for an indie who can’t afford a traditional marketing campaign. A feature on the front page will blow the traffic you’d get from a Tuber or Twitch play out of the water. But you’d only get featured if you have high sales momentum or high wishlists before launch. That’s what the pre launch marketing campaign is for. Getting on YouTube and Twitch channels is just to get the snowball rolling. The rest comes from the Steam algorithm and word of mouth.