Yeah, it became the industry standard because it rakes in mind-blowingly huge revenue for the app store owner, e.g. https://www.cultofmac.com/601492/app-store-google-play-reven.... From the article: "It’s no wonder Services — which includes App Store revenue — has become an increasingly important business for Apple as hardware sales have slowed.".
While you're correct that it costs money to run Steam, it's not _that_ much money.
https://youtube.com/watch?v=stxVBJem3Rs Here's a talk from a very old indie company, there's one section talking about how they existed pre-Steam (and other stores they use since Steam's not exclusive) and appreciate what it's enabled.
Steam isn't so much better than the competition that no one can compete with them--they just got into the market at the right time and network effects have taken over.
I mentioned probable economies of scale in a cousin comment, but I don't think they offer all that much. Do you have a % in mind that you intuitively think could be knocked off from the stores of Valve, GOG, Google, Apple, Microsoft, Salesforce App Exchange, and Amazon Appstore, all taking around 30% before you get into the fine print?
Assume a $50 game. 100,000 sales. 5 gigs.
Storage and bandwidth = $28,000 (per Amazon's calculator) Cost of doing business in N countries = use paypal = 2.9%+0.30/sale = approximately $1.75/sale = $175,000
Costs = $203,000 Revenue = $5,000,000 Ratio = 4.1%
So yeah, Valve is not the shining knight here and that 30% fee is unjustifiable. Even Epic's 12% share is still very much profitable for Epic.
The 30% fee is also nowhere comparable to wholesale pricing schema of the retail model (effectively a 40-60% fee), since that involved the sale of physical copies of goods, and the retailers had to deal with issues like shrinkage and the risk of unsold inventory.
This example is also using s3 retail pricing and paypal retail pricing, which already factors in profits for Amazon and Paypal.
None of the big marketplace's costs are anywhere near 30%.
I hate Epic for their Exclusivity, but lets not pretend that 30% Fee is nothing more than a money grab by Apple, Google, Valve and the rest of these platforms
Epic's play is to try and see if being a better looking deal for game devs will translate to being better for gamers or other groups (like linux users, open source advocates) too. We'll see. Valve has already demonstrated their goodwill towards all the groups multiple times, even if it's motivated by keeping their platform dominance.