It does for software becuase when somthing gains enough marketshare it then becomes somthing that businesses start to consider as a general option.
Like the reason Adobe gets by despite the culture for just pirating their software is becuase even piracy gives market share, and Adobe products are so commonly used that corporations feel obliged to use Adobe licences in their projects.
I’d argue that Valve does more than just take 30% as a middle man. Between Steam Input, Proton, the beta built in recording system, the Forums for every game, community system and the marketplace, having your game on Steam is a massive value generator for the consumer and by extension developers.
30% might not be what the industry standard should be, but Valve isn’t just providing a standard digital distribution service.