?? Who got a lot of money doesn’t even really need Steam. They can sell on whatever platform easily or sell directly. Big software houses started publishing on Steam because the majority of people buy there on PC … they could afford paying even a $100,000 or $1,000,000 fee to Steam or more (heck they were paying $1,000,000+ for the professional 3D Engine alone… and most still do to get premium support)
Freelancers and small software houses can’t afford paying an high fee and the world isn’t full of people willing to give the money to publish games with nothing in return. For Unreal Engine 4 … a 5% goes to Epic Games, Steam gets 30% … … some countries have low 20% to 30% taxes yes… but in the EU most countries have insane 50% to 65% taxes. That means that adding an high fee , anything above $500, could make it impossible for small and very small productions to even try selling their products on Steam. Adding a publisher to the mix with another 10% to 30% fee would mean that small software houses and freelancers could end up working hard for free, there would be no money left for them.