There are practical barriers still tho. You'll have to either maintain or outsource maintaining:
- hosting infrastructure
- CDN
- Security (both frontend and backend)
- DRM (either serial numbering or yet another hosted verification services)
- user accounts and data handling
- payment processing
And that's for a basic game, if you want feature parity with steam, add on top:
- version control and access (playtests, betas)
- version control for other platforms (Mac, Linux)
- hosting for savefile sync, achievements
- hosting for UGC (mods, screenshots, configs, recording)
- hosting and infrastructure for user livestreaming
- CDN for mods
- review (automated or manual) for mods or UGC
- legal protection and compliance against UGC
- multiplayer service infrastructure
- automated/manual moderation of game servers/lobbies
- anticheat system
- hosting for newsfeed (update announcements, news)
- and so on, you get the point...
By the time you implement the basic stuff and half of the extras, might as well pay the 30% commission and just focus on what you wanted to do: make games. Instead of having to cosplay as a sysadmin or orchestrate 15 different providers