If someone says they're not interested in dating Republicans, it doesn't mean they are any better than the average person at picking one out from a crowd.
knitwitt
Stream created and maintains a platform that gamers and developers want to use but more importantly, they've built up a reputation that people believe in and trust.
Gamers and developers are so eager to use steam because in all the years they've been operating, they still support and expand upon family sharing, have a fantastic refund policy (for consumers), don't employ aggressive exclusivity deals, don't limit download speeds behind paywalls, and provide a great review and recommendation system.
They've become successful due to this reputation, why should we punish them for that?
Valve created a fantastic entertainment product that people voluntarily choose to use. Why would you want to turn something people already love into something completely different? Counterproductive - especially when direct distribution is essentially free and universally accessible.
Developers can and almost always do close to offer their games on multiple platforms and can even choose self hosted direct distribution of they do choose. Customers can choose to purchase their games on steam, itch, epic, Microsoft, or any of the many places they're often hosted simultaneously. Steam is more often than not the choice people choose to use of their own free will because they perceive it as being the superior service.
Why do you believe excellence should be punished?