That won’t happen.
If Steam fails a competitor will rise and take over.
The majority of people need a single huge online store where to shop as the Apple App Store is proof of.
Before the App Store, Steam and Play Store the market was very small with cheaper shareware games sold on producers websites and more expensive games sold in physical shops. Nothing else. And everyone was making a lot less money. It was a less competitive market indeed and 2D and 3D engines had very high license costs that not everyone could afford, only estabilished businesses and rich people fundings the “startups” at the time.