None of this is really going to change until we end up with a situation like the EA/Apple Store conflict: a major player unable to sell a game on Windows for some reason.
Proton is them trying a different path towards severing or lessening the Windows dependence, in my opinion.
They certainly have a better card deck than Loki Entertainment used to have.
"zero" might be a bit harsh, considering that they do some things at least, compared to others who literally do nothing. Steam the platform has native Linux support, what games are natively available is visible on Store listings, and a bunch of the SDKs (all of them even maybe?) are available natively on Linux too. The situation could have been a lot worse.
Valve themselves seems to disagree with you here, considering they still have Linux native SDKs available for integration, and are releasing their own games with native Linux support.
I'm guessing if what you say is true, Valve would be the first to move towards that reality you paint, but we haven't seen that yet, I'm doubting we'll ever see that, but the ones who live will see I suppose :)